LM25117PMHE/NOPB - NATIONAL SEMICONDUCTOR

VOUT

SSRESRT

COMP

RAMP

PGND

CSG

VCCVIN

AGND

UVLO

VCCDIS

DEMB

VIN

VOUT

LM25117

Product

Folder

Sample &

Buy

Technical

Documents

Tools &

Software

Support &

Community

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

LM25117/Q1 Wide Input Range Synchronous Buck Controller With Analog Current

Monitor

1 Features 3 Description

The LM25117 is a synchronous buck controller

1• LM25117-Q1 is Qualified for Automotive intended for step-down regulator applications from a

Applications high voltage or widely varying input supply. The

• AEC-Q100 Qualified With the Following Results: control method is based upon current mode control

– Device Temperature Grade 1: -40°C to 125°C utilizing an emulated current ramp. Current mode

control provides inherent line feed-forward, cycle-by-

Ambient Operating Temperature Range cycle current limiting and ease of loop compensation.

• Emulated Peak Current Mode Control The use of an emulated control ramp reduces noise

• Wide Operating Range from 4.5 V to 42 V sensitivity of the pulse-width modulation circuit,

• Robust 3.3 A Peak Gate Drives allowing reliable control of very small duty cycles

necessary in high input voltage applications.

• Adaptive Dead-time Output Driver Control

• Free-run or Synchronizable Clock up to 750 kHz The operating frequency is programmable from 50

kHz to 750 kHz. The LM25117 drives external high-

• Optional Diode Emulation Mode side and low-side NMOS power switches with

• Programmable Output from 0.8 V adaptive dead-time control. A user-selectable diode

• Precision 1.5% Voltage Reference emulation mode enables discontinuous mode

operation for improved efficiency at light load

• Analog Current Monitor conditions. A high voltage bias regulator that allows

• Programmable Current Limit external bias supply further improves efficiency. The

• Hiccup Mode Over Current Protection LM25117’s unique analog telemetry feature provides

average output current information. Additional

• Programmable Soft-start and Tracking features include thermal shutdown, frequency

• Programmable Line Undervoltage Lockout synchronization, hiccup mode current limit and

• Programmable Switch-over to External Bias adjustable line undervoltage lockout.

Supply

• Thermal Shutdown Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)

2 Applications LM25117 HTSSOP (20) PWP 6.50 mm x 4.40 mm

LM25117-Q1 WQFN (24) RTW 4.00 mm x 4.00 mm

• Automotive Infotainment

• Industrial DC-DC Motor Drivers (1) For all available packages, see the orderable addendum at

the end of the datasheet.

• Automotive USB Power

• Telecom Server

Typical Application

An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,

intellectual property matters and other important disclaimers. PRODUCTION DATA.

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

Table of Contents

7.3 Feature Description................................................. 13

1 Features.................................................................. 17.4 Device Functional Modes........................................ 21

2 Applications ........................................................... 18 Application and Implementation ........................ 22

3 Description............................................................. 18.1 Application Information............................................ 22

4 Revision History..................................................... 28.2 Typical Applications ............................................... 22

5 Pin Configuration and Functions......................... 38.3 Detailed Design Procedure..................................... 22

6 Specifications......................................................... 58.4 Application Curves.................................................. 32

6.1 Absolute Maximum Ratings ...................................... 59 Power Supply Recommendations...................... 35

6.2 ESD Ratings (LM25117)........................................... 510 Layout................................................................... 35

6.3 ESD Ratings (LM25117-Q1)..................................... 510.1 Layout Guideline................................................... 35

6.4 Recommended Operating Conditions....................... 611 Device and Documentation Support................. 36

6.5 Thermal Information.................................................. 611.1 Community Resources.......................................... 36

6.6 Electrical Characteristics........................................... 711.2 Related Links ........................................................ 36

6.7 Switching Characteristics.......................................... 811.3 Trademarks........................................................... 36

6.8 Typical Characteristics.............................................. 911.4 Electrostatic Discharge Caution............................ 36

7 Detailed Description............................................ 11 11.5 Glossary................................................................ 36

7.1 Overview................................................................. 11 12 Mechanical, Packaging, and Orderable

7.2 Functional Block Diagram....................................... 12 Information........................................................... 36

4 Revision History

NOTE: Page numbers for previous revisions may differ from page numbers in the current version.

Changes from Revision E (March 2013) to Revision F Page

• Added Device Information and Pin Configuration and Functions sections, ESD Rating table, Feature Description,

Device Functional Modes,Application and Implementation,Power Supply Recommendations,Layout,Device and

Documentation Support , and Mechanical, Packaging, and Orderable Information sections................................................ 1

• Changed µH to µF................................................................................................................................................................ 29

Changes from Revision D (March 2013) to Revision E Page

• Changed layout of National Data Sheet to TI format ........................................................................................................... 34

Product Folder Links: LM25117 LM25117-Q1

PGND

UVLO

AGND

DEMB

RES

COMP

8 9

1211

VIN

VCC

CSG

RAMP

21222324

VCCDIS

7 10

UVLO

AGND

DEMB

RES

COMP

VIN

PGND

VCC

CSG

RAMP

VCCDIS

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

5 Pin Configuration and Functions

PWP Package

20-Pin HTSSOP

Top View

RTW Package

24-Pin WQFN

Top View

Product Folder Links: LM25117 LM25117-Q1

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

Pin Functions

PIN TYPE(1) DESCRIPTION

HTSSO WQFN NAME

P NO. NO.

1 24 UVLO I Undervoltage lockout programming pin. If the UVLO pin voltage is below 0.4V, the regulator is

in the shutdown mode with all functions disabled. If the UVLO pin voltage is greater than 0.4V

and less than 1.25V, the regulator is in standby mode with the VCC regulator operational, the

SS pin grounded, and no switching at the HO and LO outputs. If the UVLO pin voltage is above

1.25 V, the SS pin is allowed to ramp and pulse width modulated gate drive signals are

delivered to the HO and LO pins. A 20μA current source is enabled when UVLO exceeds 1.25V

and flows through the external UVLO resistors to provide hysteresis.

2 1 DEMB I Optional logic input that enables diode emulation when in the low state. In diode emulation

mode, the low-side NMOS is latched off for the remainder of the PWM cycle after detecting

reverse current flow (current flow from output to ground through the low-side NMOS). When

DEMB is high, diode emulation is disabled allowing current to flow in either direction through the

low-side NMOS. A 50kΩpull-down resistor internal to the LM25117 holds DEMB pin low and

enables diode emulation if the pin is left floating.

3 2 RES O The restart timer pin that configures the hiccup mode current limiting. A capacitor on the RES

pin determines the time the controller remains off before automatically restarting. The hiccup

mode commences when the controller experiences 256 consecutive PWM cycles of cycle-by-

cycle current limiting. After this occurs, an 10μA current source charges the RES pin capacitor

to the 1.25V threshold and restarts LM25117.

4 3 SS I An external capacitor and an internal 10μA current source set the ramp rate of the error

amplifier reference during soft-start. The SS pin is held low when VCC< 4V, UVLO < 1.25V or

during thermal shutdown.

5 4 RT I The internal oscillator is programmed with a single resistor between RT and the AGND. The

recommended maximum oscillator frequency is 750kHz. The internal oscillator can be

synchronized to an external clock by coupling a positive pulse into the RT pin through a small

coupling capacitor.

6 5 AGND G Analog ground. Return for the internal 0.8V voltage reference and analog circuits.

7 7 VCCDIS I Optional input that disables the internal VCC regulator. If VCCDIS>1.25V, the internal VCC

regulator is disabled. VCCDIS has an internal 500kΩpull-down resistor to enable the VCC

regulator when the pin is left floating. The internal 500kΩpull-down resistor can be overridden

by pulling VCCDIS above 1.25V with a resistor divider connected to an external bias supply.

8 8 FB I Feedback. Inverting input of the internal error amplifier. A resistor divider from the output to this

pin sets the output voltage level. The regulation threshold at the FB pin is 0.8V.

9 9 COMP O Output of the internal error amplifier. The loop compensation network should be connected

between this pin and the FB pin.

10 10 CM O Current monitor output. Average of the sensed inductor current is provided. Monitor directly

between CM and AGND. CM should be left floating when the pin is not used.

11 11 RAMP I PWM ramp signal. An external resistor and capacitor connected between the SW pin, the

RAMP pin and the AGND pin sets the PWM ramp slope. Proper selection of component values

produces a RAMP signal that emulates the AC component of the inductor with a slope

proportional to input supply voltage.

12 12 CS I Current sense amplifier input. Connect to the high-side of the current sense resistor.

13 13 CSG I Kelvin ground connection to the current sense resistor. Connect directly to the low-side of the

current sense resistor.

14 14 PGND G Power ground return pin for low-side NMOS gate driver. Connect directly to the low-side of the

current sense resistor.

15 15 LO O Low-side NMOS gate drive output. Connect to the gate of the low-side synchronous NMOS

transistor through a short, low inductance path.

16 16 VCC P/O/I Bias supply pin. Locally decouple to PGND using a low ESR/ESL capacitor located as close to

controller as possible.

17 18 SW I/O Switching node of the buck regulator. Connect to the bootstrap capacitor, the source terminal of

the high-side NMOS transistor and the drain terminal of the low-side NMOS through a short,

low inductance path.

18 19 HO O High-side NMOS gate drive output. Connect to the gate of the high-side NMOS transistor

through a short, low inductance path.

19 20 HB P High-side driver supply for the bootstrap gate drive. Connect to the cathode of the external

bootstrap diode and to the bootstrap capacitor. The bootstrap capacitor supplies current to

charge the high-side NMOS gate and should be placed as close to controller as possible.

(1) I = Input, O = Output, G = Ground, P = Power

Product Folder Links: LM25117 LM25117-Q1

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

Pin Functions (continued)

PIN TYPE(1) DESCRIPTION

HTSSO WQFN NAME

P NO. NO.

20 22 VIN P/I Supply voltage input source for the VCC regulator.

EP EP EP - Exposed pad of the package. Electrically isolated. Should be soldered to the ground plane to

reduce thermal resistance.

6 NC - No electrical contact.

17 NC - No electrical contact.

21 NC - No electrical contact.

23 NC - No electrical contact.

6 Specifications

6.1 Absolute Maximum Ratings

over operating free-air temperature range (unless otherwise noted)(1)

MIN MAX UNIT

VIN to AGND -0.3 45 V

SW to AGND -3.0 45 V

HB to SW -0.3 15 V

VCC to AGND(2) -0.3 15 V

HO to SW -0.3 HB+0.3 V

LO to AGND -0.3 VCC+0.3 V

FB, DEMB, RES, VCCDIS, UVLO to AGND -0.3 15 V

CM, COMP to AGND(3) -0.3 7 V

SS, RAMP, RT to AGND -0.3 7 V

CS, CSG, PGND, to AGND -0.3 0.3 V

Storage temperature, Tstg -55 150 °C

Junction Temperature -40 150 °C

(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings

only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended

Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

(2) See Application and Implementation when input supply voltage is less than the VCC voltage.

(3) These pins are output pins. As such they are not specified to have an external voltage applied.

6.2 ESD Ratings (LM25117) VALUE UNIT

Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) ±2000 V

V(ESD) Electrostatic discharge Charged-device model (CDM), per JEDEC specification JESD22- V ±750 V

C101(2)

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.

(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.

6.3 ESD Ratings (LM25117-Q1) VALUE UNIT

Human-body model (HBM), per AEC Q100-002(1) ±2000 V

V(ESD) Electrostatic discharge Charged-device model (CDM), per AEC Q100-011 ±750 V

(1) AEC Q100-002 indicates that HBM stressing shall be in accordance with the ANSI/ESDA/JEDEC JS-001 specification.

Product Folder Links: LM25117 LM25117-Q1

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

6.4 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted) (1)

MIN MAX UNIT

VIN(2) 4.5 42 V

VCC 4.5 14 V

HB to SW 4.5 14 V

Junction -40 125 °C

Temperature

(1) Recommended Operating Conditions are conditions under which operation of the device is intended to be functional, but does not

ensure specific performance limits. For specifications and test conditions see .Electrical Characteristics

(2) Minimum VIN operating voltage is defined with VCC supplied by the internal HV startup regulator and no external load on VCC. When

VCC is supplied by an external source, minimum VIN operating voltage is 4.5 V.

6.5 Thermal Information LM25117, LM25117-Q1

THERMAL METRIC(1) PWP (HTSSOP) RTW (WQFN) UNIT

20 PINS 24 PINS

RθJA Junction-to-ambient thermal resistance 40 40 °C/W

RθJC(top) Junction-to-case (top) thermal resistance 4 6 °C/W

(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application

report, SPRA953.

Product Folder Links: LM25117 LM25117-Q1

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

6.6 Electrical Characteristics

Typical limits are for TJ= 25°C only; typical values represent the most likely parametric norm at TJ= 25°C, and are provided

for reference purposes only. Minimum and maximum limits apply over the junction temperature range of –40°C to +125°C.

Unless otherwise specified, the following conditions apply: VVIN = 24 V, VVCCDIS = 0 V, RT= 25 kΩ, no load on LO & HO.

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

VIN SUPPLY

IBIAS VIN Operating Current (1) VSS = 0V 4.8 6.2 mA

VSS = 0V, VVCCDIS = 2V 0.4 0.55 mA

ISHUTDOWN VIN Shutdown Current VSS = 0V, VUVLO = 0V 16 40 µA

VCC Regulator

VCC(REG) VCC Regulation No Load 6.85 7.6 8.2 V

VCC Dropout (VIN to VCC) VVIN = 4.5V, No external load 0.05 0.14 V

VVIN = 5.0V, ICC = 20mA 0.4 0.5 V

VCC Sourcing Current Limit VVCC = 0V 30 42 mA

IVCC VCC Operating Current (1) VSS = 0V, VVCCDIS = 2V 4.0 5.0 mA

VSS = 0V, VVCCDIS = 2V, VVCC = 14V 5.8 7.3 mA

VCC Under-voltage Threshold VCC Rising 3.75 4.0 4.15 V

VCC Under-voltage Hysteresis 0.2 V

VCC Disable

VCCDIS Threshold VCCDIS Rising 1.22 1.25 1.29 V

VCCDIS Hysteresis 0.06 V

VCCDIS Input Current VVCCDIS = 0V -20 nA

VCCDIS Pull-down Resistance 500 kΩ

UVLO

UVLO Threshold UVLO Rising 1.22 1.25 1.29 V

UVLO Hysteresis Current VUVLO = 1.4V 15 20 25 µA

UVLO Shutdown Threshold UVLO Falling 0.23 0.3 V

UVLO Shutdown Hysteresis 0.1 V

Soft Start

ISS SS Current Source VSS = 0V 7 10 12 µA

SS Pull-down Resistance 13 24 Ω

Error Amplifier

VREF FB Reference Voltage Measured at FB, FB = COMP 788 800 812 mV

FB Input Bias Current VFB = 0.8V 1 nA

VOH COMP Output High Voltage ISOURCE = 3mA 2.8 V

VOL COMP Output Low Voltage ISINK = 3mA 0.26 V

AOL DC Gain 80 dB

fBW Unity Gain Bandwidth 3 MHz

PWM Comparator

tHO(OFF) Forced HO Off-time 260 320 440 ns

tON(MIN) Minimum HO On-time VVIN = 42V 100 ns

COMP to PWM comparator offset 1.2 V

Oscillator

fSW1 Frequency 1 RT= 25kΩ180 200 220 kHz

fSW2 Frequency 2 RT= 10kΩ430 480 530 kHz

RT Output Voltage 1.25 V

RT Sync Positive Threshold 2.6 3.2 3.95 V

Sync Pulse Width 100 ns

(1) Operating current does not include the current into the RTresistor.

Product Folder Links: LM25117 LM25117-Q1

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

Electrical Characteristics (continued)

Typical limits are for TJ= 25°C only; typical values represent the most likely parametric norm at TJ= 25°C, and are provided

for reference purposes only. Minimum and maximum limits apply over the junction temperature range of –40°C to +125°C.

Unless otherwise specified, the following conditions apply: VVIN = 24 V, VVCCDIS = 0 V, RT= 25 kΩ, no load on LO & HO.

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

Current Limit

VCS(TH) Cycle-by-cycle Sense Voltage VRAMP = 0, CSG to CS 106 120 135 mV

Threshold

CS Input Bias Current VCS = 0V -100 -66 µA

CSG Input Bias Current VCSG = 0V -100 -66 µA

Current Sense Amplifier Gain 10 V/V

Hiccup Mode Fault Timer 256 Cycles

RES

IRES RES Current Source 10 µA

VRES RES Threshold RES Rising 1.22 1.25 1.285 V

Diode Emulation

VIL DEMB Input Low Threshold 2.0 1.65 V

VIH DEMB Input High Threshold 2.95 2.5 V

SW Zero Cross Threshold -5 mV

DEMB Input Pull-down Resistance 50 kΩ

Current Monitor

Current Monitor Amplifier Gain CS to CM 17.5 20.5 23.5 V/V

Current Monitor Amplifier Gain Drift over Temperature -2 0 +2 %

Zero Input Offset 25 120 mV

HO Gate Driver

VOHH HO High-state Voltage Drop IHO = –100mA, VOHH = VHB - VHO 0.17 0.3 V

VOLH HO Low-state Voltage Drop IHO = 100mA, VOLH = VHO - VSW 0.1 0.2 V

HO Rise Time C-load = 1000pF (2) 6 ns

HO Fall Time C-load = 1000pF (2) 5 ns

IOHH Peak HO Source Current VHO = 0V, SW = 0V, HB = 7.6V 2.2 A

IOLH Peak HO Sink Current VHO = VHB = 7.6V 3.3 A

HB to SW Under-voltage 2.56 2.9 3.32 V

HB DC Bias Current HB - SW = 7.6V 65 100 µA

LO Gate Driver

VOHL LO High-state Voltage Drop ILO = –100mA, VOHL = VCC-VLO 0.17 0.27 V

VOLL LO Low-state Voltage Drop ILO = 100mA, VOLL = VLO 0.1 0.2 V

LO Rise Time C-load = 1000pF (2) 6 ns

LO Fall Time C-load = 1000pF (2) 5 ns

IOHL Peak LO Source Current VLO = 0V 2.5 A

IOLL Peak LO Sink Current VLO = 7.6V 3.3 A

Thermal

TSD Thermal Shutdown Temperature Rising 165 °C

Thermal Shutdown Hysteresis 25 °C

(2) High and low reference are 80% and 20% of the pulse amplitude respectively.

6.7 Switching Characteristics

over operating free-air temperature range (unless otherwise noted)

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

TDLH LO fall to HO rise delay 72 ns

No load

TDHL HO fall to LO rise delay 71 ns

Product Folder Links: LM25117 LM25117-Q1

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

6.8 Typical Characteristics

Figure 1. HO Peak Driver Current Vsoutput Voltage Figure 2. LO Peak Driver Current vs Output Voltage

Figure 3. Driver Dead Time vs VVCC Figure 4. Driver Dead Time vs Temperature

Figure 5. Forced Ho Off-Time vs Temperature Figure 6. Switching Frequency vs RT

Product Folder Links: LM25117 LM25117-Q1

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

Typical Characteristics (continued)

Figure 7. VVCC vs IVCC Figure 8. VVCC vs VVIN

Figure 9. VCS(TH) vs Temperature Figure 10. VREF vs Temperature

Figure 12. Error Amp Gain And Phase vs Frequency

Figure 11. VVCC vs Temperature

Product Folder Links: LM25117 LM25117-Q1

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

Typical Characteristics (continued)

Figure 13. VCM vs IOUT Figure 14. VCM vs VCSG-CS

7 Detailed Description

7.1 Overview

The LM25117 high voltage switching controller features all of the functions necessary to implement an efficient

high voltage buck regulator that operates over a very wide input voltage range. This easy to use controller

integrates high-side and low-side NMOS drivers. The regulator control method is based upon peak current mode

control utilizing an emulated current ramp. Peak current mode control provides inherent line feed-forward, cycle-

by-cycle current limiting and ease of loop compensation. The use of an emulated control ramp reduces noise

sensitivity of the PWM circuit, allowing reliable processing of the very small duty cycles necessary in high input

voltage applications.

The switching frequency is user programmable up to 750 kHz. The RT pin allows the switching frequency to be

programmed by a single resistor or synchronized to an external clock. Fault protection features include cycle-by-

cycle and hiccup mode current limiting, thermal shutdown and remote shutdown capability by pulling down UVLO

pin. The UVLO input enables the regulator when the input voltage reaches a user selected threshold and

provides a very low quiescent shutdown current when pulled low. A unique analog telemetry feature provides

averaged output current information, allowing various applications that need either a current monitor or current

control. The functional block diagram and typical application circuit of the LM25117 are shown in Functional

Block Diagram

The device is available in HTSSOP-20 and WQFN-24 (4mm×4mm) package featuring an exposed pad to aid in

thermal dissipation.

Product Folder Links: LM25117 LM25117-Q1

RES

AGND

REF

DISABLE

VCC

HO Driver

LO Driver

LEVEL SHIFT/

ADAPTIVE

TIMER

R Q

CLK

1.2V

DEMB

SS Current

VIN

VCC

UVLO

VCC OFF

SS HB

PGND

COMP

CSG

VCC Regulator

THERMAL

SHUTDOWN

UVLO

Shutdown

Threshold

STANDBY

VCC OFF

RES RESET

UVLO

Threshold

UVLO Hysteresis

Current

RESTART

TIMER

HICCUP MODE

FAULT TIMER

256 CYCLES

RES

Current

UVLO

VCC

STANDBY

DE_ENABLE

STANDBY

RES RESET

HICCUP

10uVCS(TH)

PWM

Comparator

C/L

Comparator

50 k:

DE_ENABLE

2.0/2.5V

OSCILLATOR/

SYNC DETECTOR

CLK

A=2

40 k:

CONDITIONER

Current Sense

Amplifier

RAMP

HO_ENABLE

ZCD

Comparator -5 mV

DIODE

EMULATION

CONTROL

LO_ENABLE

ERR

AMP

VCCDIS

500 k:

VCCDIS

Threshold

VCC OFF

DE_ENABLE

LM25117

REF

VOUT

VIN

CIN

COUT1

COUT2

RSNB

CSNB

RGH

RGL

DHB

CVCC

CCS

RCS2

RCS1

CHB

RVIN

CVIN

SYNC

CFT

CRAMP

RRAMP

RFB2

RFB1

RCOMP CCOMP

CHF

CSYNC RT

CRES

CSS

RUV2

RUV1

RCM

CCM

STANDBY

VCC OFF

HO_ENABLE

UVLO

Current Monitor

Amplifier

A=10

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

7.2 Functional Block Diagram

Product Folder Links: LM25117 LM25117-Q1

VCC

VCCDIS

LM25117

VOUT

VCCDIS resistor divider is required

when external VCC supplying voltage is

smaller than 8.5V

VCC

VCCDIS

LM25117

VOUT

VCCDIS resistor divider is required

when external VCC supplying voltage is

smaller than 8.5V

VIN

LM25117

VIN

VCC

External

VCC Supply

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

7.3 Feature Description

7.3.1 High Voltage Startup Regulator and VCC Disable

The LM25117 contains an internal high voltage bias regulator that provides the VCC bias supply for the PWM

controller and NMOS gate drivers. The VIN pin can be connected to an input voltage source as high as 42V. The

output of the VCC regulator is set to 7.6V. When the input voltage is below the VCC set-point level, the VCC

output tracks the VIN with a small dropout voltage. The output of the VCC regulator is current limited at 30mA

minimum.

Upon power-up, the regulator sources current into the capacitor connected to the VCC pin. The recommended

capacitance range for the pin VCC is 0.47µF to 10µF. When the VCC pin voltage exceeds the VCC UV threshold

and the UVLO pin is greater than UVLO threshold, the HO and LO drivers are enabled and a soft-start sequence

begins. The HO and LO drivers remain enabled until either the VCC pin voltage falls below VCC UV threshold,

the UVLO pin voltage falls below UVLO threshold, hiccup mode is activated or the die temperature exceeds the

thermal shutdown threshold. Enabling/Disabling the IC by controlling UVLO is recommended in most of cases.

An output voltage derived bias supply can be applied to the VCC pin to reduce the controller power dissipation at

higher input voltage. The VCCDIS input can be used to disable the internal VCC regulator when external biasing

is supplied. The externally supplied bias should be coupled to the VCC pin through a diode, preferably a

Schottky diode. If the VCCDIS pin voltage exceeds the VCCDIS threshold, the internal VCC regulator is disabled.

VCCDIS has a 500kΩinternal pull-down resistor to ground for normal operation with no external bias.

The VCC regulator series pass transistor includes a diode between VCC (Anode) and VIN (Cathode) that should

not be forward biased in normal operation. If the voltage of the external bias supply is greater than the VIN pin

voltage, an external blocking diode is required from the input power supply to the VIN pin to prevent the external

bias supply from passing current to the input supply through VCC.

Figure 15. VIN Configuration For VVIN<VVCC

For VOUT between 5V and 14.5V, the output can be connected directly to VCC through a diode.

Figure 16. External VCC Supply For 5 V< VOUT<14.5 V

For VOUT < 5V, a bias winding on the output inductor can be added to generate the external VCC supply voltage.

Figure 17. External VCC Supply For VOUT <5 V

Product Folder Links: LM25117 LM25117-Q1

LM25117

VIN

UVLO

Shutdown

Threshold SHUTDOWN

UVLO

Threshold

UVLO Hysteresis

Current

UVLO

CFT

RUV2

RUV1

STANDBY

VCC

LM25117

VOUT

Zener

R1 is required to limit maximum reverse zener current

30 k: minimum resistive loss at VCC

guarantees minimum reverse zener current

30 k:

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

Feature Description (continued)

For 14.5 V <VOUT, the external supply voltage can be regulated by using a series Zener diode from the output to

VCC.

Figure 18. External VCC Supply For 14.5 V <VOUT

In high input voltage applications, extra care should be taken to ensure the VIN pin does not exceed the absolute

maximum voltage rating of 45V. During line or load transients, voltage ringing on the VIN that exceeds the

Absolute Maximum Rating can damage the IC. Both careful PC board layout and the use of quality bypass

capacitors located close to the VIN and AGND pin are essential. Adding an R-C filter (RVIN, CVIN) on VIN is

optional and helps to prevent faulty operation caused by poor PC board layout and high frequency switching

noise injection. The recommended capacitance and resistance range are 0.1µF to 10µF and 1Ωto 10Ω.

7.3.2 UVLO

The LM25117 contains a dual level UVLO (under-voltage lockout) circuit. When the UVLO is less than 0.4 V, the

LM25117 is in shutdown mode. The shutdown comparator provides 100mV of hysteresis to avoid chatter during

transitions. When the UVLO pin voltage is greater than 0.4 V but less than 1.25 V, the controller is in standby

mode. In the standby mode, the VCC bias regulator is active but the HO and LO drivers are disabled and the SS

pin is held low. This feature allows the UVLO pin to be used as a remote shutdown function by pulling the UVLO

pin down below 0.4V with an external open collector or open drain device. When the VCC pin exceeds its under-

voltage lockout threshold and the UVLO pin voltage is greater than 1.25V, the HO and LO drivers are enabled

and normal operation begins.

Figure 19. UVLO Configuration

The UVLO pin should not be left floating. An external UVLO set-point voltage divider from the VIN to AGND is

used to set the minimum input operating voltage of the regulator. The divider must be designed such that the

voltage at the UVLO pin is greater than 1.25V and never exceeds 15V when the input voltage is in the desired

operating range. If necessary, the UVLO pin can be clamped with a Zener diode.

UVLO hysteresis is accomplished with an internal 20μA current source that is switched on or off into the

impedance of the UVLO set-point divider. When the UVLO pin voltage exceeds the 1.25 V threshold, the current

source is enabled to quickly raise the voltage at the UVLO pin. When the UVLO pin voltage falls below the 1.25

V threshold, the current source is disabled causing the voltage at the UVLO pin to quickly fall. The use of a CFT

capacitor in parallel with RUV1 helps to minimize switching noise injection into UVLO pin, but it may slow down

the falling speed of the UVLO pin when the 20μA current source is disabled. The recommended range for CFT is

10pF to 220pF.

Product Folder Links: LM25117 LM25117-Q1

5.2 x 109

RT = - 948 [5]

fSW

1.25V x RUV2

RUV1 = VIN(STARTUP) - 1.25V [5]

VHYS

RUV2 = 20 µA[5]

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

Feature Description (continued)

The values of RUV1 and RUV2 can be determined from the following equations:

(1)

(2)

Where VHYS is the desired UVLO hysteresis and VIN(STARTUP) is the desired startup voltage of the regulator during

turn-on.

7.3.3 Oscillator And Sync Capability

The LM25117 switching frequency is programmed by a single external resistor connected between the RT pin

and the AGND pin. The resistor should be located very close to the device and connected directly to the RT and

AGND pins. To set a desired switching frequency (fSW), the resistor value can be calculated from the following

equation:

(3)

The RT pin can be used to synchronize the internal oscillator to an external clock. The internal oscillator can be

synchronized by AC coupling a positive edge into the RT pin. The voltage at the RT pin is nominally 1.25 V and

the voltage at the RT pin must exceed the RT Sync Positive Threshold to trip the internal synchronization pulse

detector. A 5 V amplitude pulse signal coupled through 100pF capacitor is a good starting point. The frequency

of the external synchronization pulse is recommended to be within +/-10% of the frequency programmed by the

RT resistor but will operate to +100/-40% of the programmed frequency. Care should be taken to make sure that

the RT pin voltage does not go below -0.3V at the falling edge of the external pulse. This may limit the duty cycle

of external synchronization pulse.

The RTresistor is always required, whether the oscillator is free running or externally synchronized.

7.3.4 Ramp Generator and Emulated Current Sense

The ramp signal used in the pulse width modulator for traditional current mode control is typically derived directly

from the high-side switch current. This switch current corresponds to the positive slope portion of the inductor

current. Using this signal for the PWM ramp simplifies the control loop transfer function to a single pole response

and provides inherent input voltage feed-forward compensation.

The disadvantage of using the high-side switch current signal for PWM control is the large leading edge spike

due to circuit parasitics that must be filtered or blanked. Minimum achievable pulse width is limited by the

filtering, blanking time and propagation delay with a high-side current sensing scheme.

In the applications where the input voltage may be relatively large in comparison to the output voltage, controlling

small pulse widths and duty cycles are necessary for regulation. The LM25117 utilizes a unique ramp generator

which does not actually measure the high-side switch current but rather reconstructs the signal. Representing or

emulating the inductor current provides a ramp signal to the PWM comparator that is free of leading edge spikes

and measurement or filtering delays, while maintaining the advantages of traditional peak current mode control.

Product Folder Links: LM25117 LM25117-Q1

RRAMP x CRAMP x RS x AS

K =

HO_ENABLE

RAMP

CSG

AS=10

RRAMP CRAMP

RSIL

10 xVCS(TH)

Current Limit

Comparator

Current Sense

Amplifier

LM25117

Sample and Hold

DC Level

tON

ILO x RS x 10

Additional Slope

VIN x tON

RRAMP x CRAMP

RAMPPK =

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

Feature Description (continued)

The current reconstruction is comprised of two elements: a sample-and-hold DC level and the emulated inductor

current ramp as shown in Figure 20. The sample-and-hold DC level is derived from a measurement of the

recirculating current flowing through the current sense resistor. The voltage across the sense resistor is sampled

and held just prior to the onset of the next conduction interval of the high-side switch. The current sense amplifier

with a gain of 10 and sample-and-hold circuit provide the DC level of the reconstructed current signal as shown

in Figure 21.

Figure 20. Composition of Emulated Current Sense Signal

Figure 21. Ramp Generator and Current Limit Circuit

The positive slope inductor current ramp is emulated by CRAMP connected between RAMP and AGND and RRAMP

connected between SW and RAMP. RRAMP should not be connected to VIN directly because the RAMP pin

absolute maximum voltage rating could be exceeded under high input voltage conditions. CRAMP is discharged by

an internal switch during the off-time and must be fully discharged during the minimum off-time. This limits the

ramp capacitor to be less than 2nF. A good quality, thermally stable ceramic capacitor is recommended for

CRAMP.

The selection of RRAMP and CRAMP can be simplified by adopting a K factor, which is defined as:

(4)

Where ASis the current sense amplifier gain which is normally 10. By choosing 1 as the K factor, the regulator

removes any error after one switching cycle and the design procedure is simplified. See Application Information

for detailed information.

Product Folder Links: LM25117 LM25117-Q1

10 µA

CSS x 0.8V

tSS = [sec]

FP2 = 1

CCOMP x CHF

CCOMP + CHF

2S x RCOMP x¹

§[Hz]

2Sx RCOMP x CCOMP

FZ = [Hz]

FP1 = 0 [Hz]

VOUT

COMP

LM25117

RFB2

RFB1

RCOMP CCOMP

CHF

REF

Error

Amplifier

Type 2 Compensation

Components

PWM

Comparator

RAMP Generator

Output

(optional)

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

Feature Description (continued)

7.3.5 Error Amplifier and PWM Comparator

The internal high-gain error amplifier generates an error signal proportional to the difference between the FB pin

voltage and the internal precision 0.8V reference. The output of error amplifier is connected to the COMP pin

allowing the user to provide Type 2 loop compensation components, RCOMP, CCOMP and optional CHF.

Figure 22. Feedback Configuration and PWM Comparator

RCOMP, CCOMP and CHF configure the error amplifier gain and phase characteristics to achieve a stable voltage

loop gain. This network creates a pole at DC (FP1), a mid-band zero (FZ) for phase boost, and a high frequency

pole (FP2). The recommended range of RCOMP is 2kΩto 40kΩ. See Application Information for detailed

information.

(5)

(6)

(7)

The PWM comparator compares the emulated current sense signal from Ramp Generator to the voltage at the

COMP pin through a 1.2 V internal voltage drop and terminates the present cycle when the emulated current

sense signal is greater than VCOMP - 1.2 V.

7.3.6 Soft-Start

The soft-start feature allows the regulator to gradually reach the steady state operating point, thus reducing

startup stresses and surges. The LM25117 regulates the FB pin to the SS pin voltage or the internal 0.8V

reference, whichever is lower. The internal 10µA soft-start current source gradually increases the voltage on an

external soft-start capacitor connected to the SS pin. This results in a gradual rise of the output voltage. Soft-start

time (tss) can be calculated from the following equation:

(8)

The LM25117 can track the output of a master power supply during soft-start by connecting a voltage divider

from the output of master power supply to the SS pin. At the beginning of the soft-start sequence, VSS should be

allowed to go below 25mV by the internal SS pull-down switch. During soft-start period, when SS pin voltage is

less than 0.8V, the LM25117 forces diode emulation for startup into a pre-biased load. If the tracking feature is

desired, connect the DEMB pin to GND or leave the pin floating.

Product Folder Links: LM25117 LM25117-Q1

RSLO

VIN(MAX) x tON(MIN)

ILIM_PK = VCS(TH) [A]

IOUT IPP

fSW

VIN

IPP = 1 - VOUT

VOUT x

LO x fSW [A]

IPP

IL(MAX)_AVE = IL(MAX)_PK -[A]

VOUT

fSW x AS x RS x RRAMP x CRAMP

+ IPP -

VCS(TH)

IL(MAX)_PK =[A]

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

Feature Description (continued)

7.3.7 Cycle-By-Cycle Current Limit

The LM25117 contains a current limit monitoring scheme to protect the regulator from possible over-current

conditions as shown in Figure 21. If the emulated ramp signal exceeds 1.2 V, the present cycle is terminated. For

the case where the switch current overshoots when the inductor is saturated or the output is shorted to ground,

the sample-and-hold circuit detects the excess recirculating current before the high-side NMOS driver is turned

on again. The high-side NMOS driver is disabled and will skip pulses until the current has decayed below the

current limit threshold. This approach prevents current runaway conditions since the inductor current is forced to

decay to a controlled level following any current overshoot. Maximum peak inductor current can be calculated as:

(9)

(10)

Where IPP represents inductor peak to peak ripple current in Figure 23, and is defined as:

(11)

Figure 23. Inductor Current

During an output short condition, the worst case peak inductor current is limited to:

(12)

Where tON(MIN) is the minimum HO on-time.

In most of cases, especially if the output voltage is relatively high, it is recommended that a soft-saturating

inductor such as a powder core device is used. If a sharp-saturating inductor is used, the inductor saturation

level must be above ILIM_PK. The temperatures of the NMOS devices, RSand inductor should be checked under

this output short condition.

7.3.8 Hiccup Mode Current Limiting

To further protect the regulator during prolonged current limit conditions, LM25117 provides a hiccup mode

current limit. An internal hiccup mode fault timer counts the PWM clock cycles during which cycle-by-cycle

current limiting occurs. When the hiccup mode fault timer detects 256 consecutive cycles of current limiting, an

internal restart timer forces the controller to enter a low power dissipation standby mode and starts sourcing

10μA current into the RES pin capacitor CRES. In this standby mode, HO and LO outputs are disabled and the

soft-start capacitor CSS is discharged.

Product Folder Links: LM25117 LM25117-Q1

RES

LM25117

VCC

CRES

RES

LM25117

RES

LM25117

VCC

(a) Hiccup Mode

Current Limit (b) Latch-off Mode

Current Limit (c) Cycle-by-cycle

Current Limit

RES

RESTART

TIMER

HICCUP MODE

FAULT TIMER

256 CYCLES

RES

Current

STANDBY

HICCUP

Current Limit

Comparator

CRES

LM25117

RES 0V

1.25V RES Threshold

0.8V REF

Current Limit

Detected

Current Limit

persists during 256

consecutive cycles

tSS

tRES

IRES = 10 µA

ISS = 10 µA

10 PA

CRES x 1.25V

tRES = [sec]

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

Feature Description (continued)

CRES is connected from RES pin to AGND and determines the time (tRES) in which the LM25117 remains in the

standby before automatically restarting. When the RES pin voltage exceeds the 1.25 V RES threshold, RES

capacitor is discharged and a soft-start sequence begins. tRES can be calculated from the following equation:

(13)

Figure 24. Hiccup Mode Current Limit Timing Diagram

Figure 25. Hiccup Mode Current Limit Circuit

The RES pin can also be configured for latch-off mode current limiting or non-hiccup mode cycle-by-cycle current

limiting. If the RES pin is tied to VCC or a voltage greater than the RES threshold at initial power-on, the restart

timer is disabled and the regulator operates with non-hiccup mode cycle-by-cycle current limit. If the RES pin is

tied to GND, the regulator enters into the standby mode after 256 consecutive cycles of current limiting and then

never restarts until UVLO shutdown is cycled. The restart timer is configured during initial power-on when UVLO

is above the UVLO threshold and VCC is above the VCC UV threshold.

Figure 26. Res Configurations

Product Folder Links: LM25117 LM25117-Q1

( ) [ ]

CM _ AVE PEAK VALLEY S S

V I I R A V= + ´ ´

AM = 2

40 k:

RCM

CCM

Current Monitor

Amplifier

Current Sense

Amplifier Output LM25117

CONDITIONER

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

Feature Description (continued)

7.3.9 HO and LO Drivers

The LM25117 contains high current NMOS drivers and an associated high-side level shifter to drive the external

high-side NMOS device. This high-side gate driver works in conjunction with an external diode DHB, and

bootstrap capacitor CHB. A 0.1μF or larger ceramic capacitor, connected with short traces between the HB and

SW pin, is recommended. During the off-time of the high-side NMOS driver, the SW pin voltage is approximately

0V and the CHB is charged from VCC through the DHB. When operating with a high PWM duty cycle, the high-

side NMOS device is forced off each cycle for 320ns to ensure that CHB is recharged.

The LO and HO outputs are controlled with an adaptive dead-time methodology which insures that both outputs

are never enabled at the same time. When the controller commands HO to be enabled, the adaptive dead-time

logic first disables LO and waits for the LO voltage to drop. HO is then enabled after a small delay (LO Fall to HO

Rise Delay). Similarly, the LO turn-on is delayed until the HO voltage has discharged. LO is then enabled after a

small delay (HO Fall to LO Rise Delay). This technique insures adequate dead-time for any size NMOS device,

especially when VCC is supplied by a higher external voltage source. The adaptive dead-time circuitry monitors

the voltages of HO and LO outputs and insures the dead-time between the HO and LO outputs. Adding a gate

resister, RGH or RGL, may decrease the effective dead-time.

Care should be exercised in selecting an output NMOS device with the appropriate threshold voltage, especially

if VCC is supplied by an external bias supply voltage below the VCC regulation level. During startup at low input

voltages, the low-side NMOS device gate plateau voltage should be lower than the VCC under-voltage lockout

threshold. Otherwise, there may be insufficient VCC voltage to completely enhance the NMOS device as the

VCC under-voltage lockout is released during startup. If the high-side NMOS drive voltage is lower than the high-

side NMOS device gate plateau voltage during startup, the regulator may not start or it may hang up momentarily

in a high power dissipation state. This condition can be addressed by selecting an NMOS device with a lower

threshold voltage. This situation can be avoided if the minimum input voltage programmed by the UVLO resistor

is above the VCC regulation level.

7.3.10 Current Monitor

The LM25117 provides average output current information, enabling various applications requiring monitoring or

control of the output current.

Figure 27. Current Monitor

The average of CM output can be calculated by:

(14)

The current monitor output is only valid in continuous conduction operation. The current monitor has a limited

bandwidth of approximately one tenth of fSW. Adding an R-C filter, RCM and CCM, on the output of current monitor

with the cut off frequency below one tenth of fSW is recommended to attenuate sampling noise.

Product Folder Links: LM25117 LM25117-Q1

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

Feature Description (continued)

7.3.11 Maximum Duty Cycle

When operating with a high PWM duty cycle, the high-side NMOS device is forced off each cycle for 320ns to

ensure that CHB is recharged and to allow time to sample and hold the current in the low-side NMOS FET. This

forced off-time limits the maximum duty cycle of the controller. When designing a regulator with high switching

frequency and high duty cycle requirements, a check should be made of the required maximum duty cycle

against the graph shown in Figure 28. The actual maximum duty cycle varies with the switching frequency as

follows:

Figure 28. Maximum Duty Cycle vs Switching Frequency

7.3.12 Thermal Protection

Internal thermal shutdown circuitry is provided to protect the controller in the event the maximum junction

temperature is exceeded. When activated, typically at 165°C, the controller is forced into a low power shutdown

mode, disabling the output drivers and the VCC regulator. This feature is designed to prevent overheating and

destroying the device.

7.4 Device Functional Modes

7.4.1 Diode Emulation

A fully synchronous buck regulator implemented with a freewheeling NMOS rather than a diode has the

capability to sink current from the output in certain conditions such as light load, over-voltage or pre-bias startup.

The LM25117 provides a diode emulation feature that can be enabled to prevent reverse current flow in the low-

side NMOS device. When configured for diode emulation, the low-side NMOS driver is disabled when SW pin

voltage is greater than -5mV during the off-time of the high-side NMOS driver, preventing reverse current flow.

A benefit of the diode emulation is lower power loss at no load or light load conditions. The negative effect of

diode emulation is degraded light load transient response.

The diode emulation feature is configured with the DEMB pin. To enable diode emulation, connect the DEMB pin

to GND or leave the pin floating. If continuous conduction operation is desired, the DEMB pin should be tied to a

voltage greater than 3V and may be connected to VCC. The LM25117 forces the regulator to operate in diode

emulation mode when SS pin voltage is less than the internal 0.8 V reference, allowing for startup into a pre-

biased load with the continuous conduction configuration.

Product Folder Links: LM25117 LM25117-Q1

RLOAD

RS x AS

Where AM (Modulator DC gain) = ,

ZZ_ESR

1 +

VOUT

VCOMP = AM x

1+ s

ZP_LF

§¹

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

The LM25117 is a step-down dc-dc controller. The device is typically used to convert a higher dc voltage to a

lower dc voltage. Use the following design procedure to select component values. Alternately, use the

WEBENCH® software to generate a complete design. The WEBENCH software uses an iterative design

procedure and accesses a comprehensive database of components when generating a design.

8.2 Typical Applications

Figure 29. 3.3 V, 9 A Typical Application Schematic

8.3 Detailed Design Procedure

8.3.1 Feedback Compensation

Open loop response of the regulator is defined as the product of modulator transfer function and feedback

transfer function. When plotted on a dB scale, the open loop gain is shown as the sum of modulator gain and

feedback gain.

The modulator transfer function includes a power stage transfer function with an embedded current loop and can

be simplified as one pole and one zero system as shown in the following equations.

(15)

(16)

Product Folder Links: LM25117 LM25117-Q1

K - 0.5

fSW

Zp_HF =

2 x ' x RS x RFB2 x AS x COUT

RCOMP

fCROSS = [Hz]

RFB2 x (CCOMP + CHF)

Where AFB (Feedback DC gain) = ,

RCOMP x CCOMP

wZ_EA (Low frequency zero) = ,

RCOMP x CHF

wP_EA (High frequency pole) =

AFB x

ZP_EA

VOUT

VCOMP

-ZZ_EA

1 +

s x (1+ )

RLOAD x COUT

ZP_LF (Load pole) =

ZZ_ESR (ESR zero) = 1

RESR x COUT ,

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

Detailed Design Procedure (continued)

(17)

(18)

If the ESR of COUT (RESR) is very small, the modulator transfer function can be further simplified to a one pole

system and the voltage loop can be closed with only two loop compensation components, RCOMP and CCOMP,

leaving a single pole response at the crossover frequency. A single pole response at the crossover frequency

yields a very stable loop with 90 degrees of phase margin.

The feedback transfer function includes the feedback resistor divider and loop compensation of the error

amplifier. RCOMP, CCOMP and optional CHF configure the error amplifier gain and phase characteristics and create

a pole at origin, a low frequency zero and a high frequency pole. This is shown mathematically in the following

equations.

(19)

(20)

The pole at the origin minimizes output steady state error. The low frequency zero should be placed to cancel the

load pole of the modulator. The high frequency pole can be used to cancel the zero created by the output

capacitor ESR or to decrease noise susceptibility of the error amplifier. By placing the low frequency zero an

order of magnitude less than the crossover frequency, the maximum amount of phase boost can be achieved at

the crossover frequency. The high frequency pole should be placed well beyond the crossover frequency since

the addition of CHF adds a pole in the feedback transfer function.

The crossover frequency (loop bandwidth) is usually selected between one twentieth and one fifth of the fSW. In a

simplified formula, the crossover frequency can be defined as:

(21)

For higher crossover frequency, RCOMP can be increased, while proportionally decreasing CCOMP. Conversely,

decreasing RCOMP while proportionally increasing CCOMP, results in lower bandwidth while keeping the same zero

frequency in the feedback transfer function.

The sampled gain inductor pole is inversely proportional to the K factor, which is defined as:

(22)

The maximum achievable loop bandwidth, in fact, is limited by this sampled gain inductor pole. In traditional

current mode control, the maximum achievable loop bandwidth varies with input voltage. With the LM25117’s

unique slope compensation scheme, the sampled gain inductor pole is independent of changes to the input

voltage. This frees the user from additional concerns in wide varying input range applications and is an

advantage of the LM25117.

Product Folder Links: LM25117 LM25117-Q1

= 1 - K

dl0

dl1

Steady-State

Inductor

Current

dI0

dI1

tON

Inductor Current with

Initial Perturbation

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

Detailed Design Procedure (continued)

If the sampled gain inductor pole or the ESR zero is close to the crossover frequency, it is recommended that the

comprehensive formulas in Table 1 be used and the stability should be checked by a network analyzer. The

modulator transfer function can be measured and the feedback transfer function can be configured for the

desired open loop transfer function. If a network analyzer is not available, step load transient tests can be

performed to verify acceptable performance. The step load goal is minimum overshoot/undershoot with a

damped response.

8.3.2 Sub-Harmonic Oscillation

Peak current mode regulators can exhibit unstable behavior when operating above 50% duty cycle. This

behavior is known as sub-harmonic oscillation and is characterized by alternating wide and narrow pulses at the

SW pin. Sub-harmonic oscillation can be prevented by adding an additional voltage ramp (slope compensation)

on top of the sensed inductor current shown in Figure 20. By choosing K≥1, the regulator will not be subject to

sub-harmonic oscillation caused by a varying input voltage.

In time-domain analysis, the steady-state inductor current starts and ends at the same value during one clock

cycle. If the magnitude of the end-of-cycle current error, dI1, caused by an initial perturbation, dI0, is less than the

magnitude of dI0or dI1/dI0> -1, the perturbation naturally disappears after a few cycles. When dI1/dI0< -1, the

initial perturbation does not disappear, resulting in sub-harmonic oscillation in steady-state operation.

Figure 30. Effect of Initial Perturbation when dl1/dl0< -1

dI1/dI0can be calculated by:

(23)

The relationship between dI1/dI0and K factor is illustrated graphically in Figure 31.

Figure 31. dl1/dl0vs K Factor

The minimum value of K is 0.5. When K<0.5, the amplitude of dI1is greater than the amplitude of dI0and any

initial perturbation results in sub-harmonic oscillation. If K=1, any initial perturbation will be removed in one

switching cycle. This is known as one-cycle damping. When -1<dl1/dl0<0, any initial perturbation will be under-

damped. Any perturbation will be over-damped when 0<dl1/dl0<1.

Product Folder Links: LM25117 LM25117-Q1

5.2 x 109

RT = 230 x 103- 948 = 21.7 k:

S(K-0.5)

Q =

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

Detailed Design Procedure (continued)

In the frequency-domain, Q, the quality factor of the sampling gain term in the modulator transfer function, is

used to predict the tendency for sub-harmonic oscillation, which is defined as:

(24)

The relationship between Q and K factor is illustrated graphically in Figure 32.

Figure 32. Sampling Gain Q vs K Factor

The minimum value of K is 0.5 again. This is the same as time domain analysis result. When K<0.5, the regulator

is unstable. High gain peaking at 0.5 results in sub-harmonic oscillation at FSW/2. When K=1, one-cycle damping

is realized. Q is equal to 0.673 at this point. A higher K factor may introduce additional phase shift by moving the

sampled gain inductor pole closer to the crossover frequency, but will help reduce noise sensitivity in the current

loop. The maximum allowable value of K factor can be calculated by the Maximum Crossover Frequency

equation in Table 1.

8.3.3 Design Requirements

DESIGN PARAMETER EXAMPLE VALUE

Output Voltage VOUT 3.3 V

Full Load Current IOUT 9 A

Minimum Input Voltage VIN(MIN) 6 V

Maximum Input Voltage VIN(MAX) 36 V

Switching Frequency fSW 230 kHz

Diode Emulation Yes

External VCC Supply No

8.3.4 Timing Resistor RT

Generally, higher frequency applications are smaller but have higher losses. Operation at 230 kHz was selected

for this example as a reasonable compromise between small size and high efficiency. The value of RTfor 230

kHz switching frequency can be calculated from Equation 3.

(25)

A standard value of 22.1kΩwas chosen for RT.

Product Folder Links: LM25117 LM25117-Q1

§36V

PRS = 1 - x 9A2 x 8 m: = 0.59W

3.3V

VIN(MAX)

PRS = 1 - IOUT2 x RS

VOUT x[W]

9A x 1.5 + 230 kHz x 6.8 µH

3.3 x 1

RS = 0.12V = 7.9 m:

0.95A

RS = VCS(TH) >:@

IOUT(MAX) + fSW x LO

VOUT x K IPP

§36V

IPP(MAX) = x 1 - 3.3V

3.3V

6.8 PH x 230 kHz = 1.9A

§36V

LO = x 1 - 3.3V

3.3V

9A x 0.2 x 230 kHz = 7.2 PH

( )

OUT OUT

PP(MAX) SW IN MAX

V V

L 1 [H]

I f V

æ ö

ç ÷

= ´ -

ç ÷

´è ø

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

8.3.5 Output Inductor LO

The maximum inductor ripple current occurs at the maximum input voltage. Typically, 20% to 40% of the full load

current is a good compromise between core loss and copper loss of the inductor. Higher ripple current allows for

a smaller inductor size, but places more of a burden on the output capacitor to smooth the ripple voltage on the

output. For this example, a ripple current of 20% of 9A was chosen. Knowing the switching frequency, maximum

ripple current, maximum input voltage and the nominal output voltage, the inductor value can be calculated as

follows:

(26)

(27)

The closest standard value of 6.8μH was chosen for LO. Using the value of 6.8μH for LO, calculate IPP again. This

step is necessary if the chosen value of LOdiffers significantly from the calculated value.

From Equation 11,

(28)

At the minimum input voltage, this value is 0.95A.

8.3.6 Diode Emulation Function

The DEMB pin is left floating since this example uses diode emulation to reduce the power loss under no load or

light load conditions.

8.3.7 Current Sense Resistor RS

The performance of the converter will vary depending on the K value. For this example, K=1 was chosen to

control sub-harmonic oscillation and achieve one-cycle damping. The maximum output current capability

(IOUT(MAX)) should be 20~50% higher than the required output current, to account for tolerances and ripple

current. For this example, 150% of 9A was chosen. The current sense resistor value can be calculated from

Equation 9 and Equation 10 as follows:

(29)

(30)

A value of 8mΩwas chosen for RS. A larger value resistor can be placed in parallel with RSto adjust the

maximum output current capability. The sense resistor must be rated to handle the power dissipation at

maximum input voltage when current flows through the low-side NMOS for the majority of the PWM cycle. The

maximum power dissipation of RScan be calculated as:

(31)

(32)

Product Folder Links: LM25117 LM25117-Q1

PDC (Low-Side) = (1 ± D) x (IOUT2 x RDS(ON) x 1.3) [W]

PDC (High-Side) = D x (IOUT2 x RDS(ON) x 1.3) [W]

1.25V x 50 k:

5.7V - 1.25V

RUV1 = = 14.0 k:

20 µA

RUV2 = = 50 k:

6.8 PH

1 x 820 pF x 8 m:x 10

RRAMP = = 104 k:

K x CRAMP x RSx AS

RRAMP = [:@

8 m:6.8 PH

36V x 100 ns

ILIM_PK = 0.12V = 15.5A

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

The worst case peak inductor current under the output short condition can be calculated from Equation 12 as

follows:

(33)

Where tON(MIN) is normally 100ns.

8.3.8 Current Sense Filter RCS and CCS

The LM25117 itself is not affected by the large leading edge spike because it samples valley current just prior to

the onset of the high-side switch. A current sense filter is used to minimize a noise injection from any external

noise sources. In general, a current sense filter is not necessary. In this example, a current sense filter is not

used

Adding RCS resistor changes the current sense amplifier gain which is defined as AS=10k / (1k+RCS). A small

value of RCS resistor below 100Ωis recommended to minimize the gain change which is caused by the

temperature coefficient difference between internal and external resistors.

8.3.9 Ramp Resistor RRAMP and Ramp Capacitor CRAMP

The positive slope of the inductor current ramp signal is emulated by RRAMP and CRAMP. For this example, the

value of CRAMP was set at the standard capacitor value of 820pF. With the inductor, sense resistor and the K

factor selected, the value of RRAMP can be calculated from Equation 4 as follows:

(34)

(35)

The standard value of 105 kΩwas selected for RRAMP.

8.3.10 UVLO Divider RUV2, RUV1 and CFT

The desired startup voltage and the hysteresis are set by the voltage divider RUV1 and RUV2. Capacitor CFT

provides filtering for the divider. For this design, the startup voltage was set to 5.7V, 0.3V below VIN(MIN). VHYS

was set to 1V. The value of RUV1, RUV2 can be calculated from Equation 1 and Equation 2 as follows:

(36)

(37)

The standard value of 50kΩwas selected for RUV2. RUV1 was selected to be 14kΩ. A value of 100pF was chosen

for CFT.

8.3.11 VCC Disable and External VCC Supply

In this example, VCCDIS is left floating to enable the internal VCC regulator.

8.3.12 Power Switches QHand QL

Selection of the power NMOS devices is governed by the same trade-offs as switching frequency. Breaking

down the losses in the high-side and low-side NMOS devices is one way to compare the relative efficiencies of

different devices. Losses in the power NMOS devices can be broken down into conduction loss, gate charging

loss, and switching loss.

Conduction loss PDC is approximately:

(38)

(39)

Product Folder Links: LM25117 LM25117-Q1

CHB Qg

'VHB

t[F]

PSW = 0.5 x VIN x IOUT x (tR + tF) x fSW [W]

PGC = n x VVCC x Qg x fSW [W]

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

Where D is the duty cycle and the factor of 1.3 accounts for the increase in the NMOS device on-resistance due

to heating. Alternatively, the factor of 1.3 can be eliminated and the high temperature on-resistance of the NMOS

device can be estimated using the RDS(ON) vs Temperature curves in the MOSFET datasheet.

Gate charging loss (PGC) results from the current driving the gate capacitance of the power NMOS devices and is

approximated as:

(40)

Qg refers to the total gate charge of an individual NMOS device, and ‘n’ is the number of NMOS devices. Gate

charge loss differs from conduction and switching losses in that the actual dissipation occurs in the controller IC.

Switching loss (PSW) occurs during the brief transition period as the high-side NMOS device turns on and off.

During the transition period both current and voltage are present in the channel of the NMOS device. The

switching loss can be approximated as:

(41)

tRand tFare the rise and fall times of the high-side NMOS device. The rise and fall times are usually mentioned

in the MOSFET datasheet or can be empirically observed with an oscilloscope. Switching loss is calculated for

the high-side NMOS device only. Switching loss in the low-side NMOS device is negligible because the body

diode of the low-side NMOS device turns on before and after the low-side NMOS device switches. For this

example, the maximum drain-to-source voltage applied to either NMOS device is 36V. The selected NMOS

devices must be able to withstand 36V plus any ringing from drain to source and must be able to handle at least

the VCC voltage plus any ringing from gate to source.

8.3.13 Snubber Components RSNB and CSNB

A resistor-capacitor snubber network across the low-side NMOS device reduces ringing and spikes at the

switching node. Excessive ringing and spikes can cause erratic operation and can couple noise to the output

voltage. Selecting the values for the snubber is best accomplished through empirical methods. First, make sure

the lead lengths for the snubber connections are very short. Start with a resistor value between 5 and 50Ω.

Increasing the value of the snubber capacitor results in more damping, but higher snubber losses. Select a

minimum value for the snubber capacitor that provides adequate damping of the spikes on the switch waveform

at heavy load. A snubber may not be necessary with an optimized layout.

8.3.14 Bootstrap Capacitor CHB and Bootstrap Diode DHB

The bootstrap capacitor between the HB and SW pin supplies the gate current to charge the high-side NMOS

device gate during each cycle’s turn-on and also supplies recovery charge for the bootstrap diode. These current

peaks can be several amperes. The recommended value of the bootstrap capacitor is at least 0.1μF. CHB should

be a good quality, low ESR, ceramic capacitor located at the pins of the IC to minimize potentially damaging

voltage transients caused by trace inductance. The absolute minimum value for the bootstrap capacitor is

calculated as:

(42)

Where Qg is the high-side NMOS gate charge and ΔVHB is the tolerable voltage droop on CHB, which is typically

less than 5% of VCC or 0.15V conservatively. A value of 0.47μF was selected for this design.

Product Folder Links: LM25117 LM25117-Q1

0.047 µF x 0.8V

tSS = 10 µA= 3.8 ms

'VIN = 4 x 230 kHz x 2.2 PFx 7

9 A = 0.63 V

'VIN = 4 x x CIN

fSW

IOUT [V]

8 x 230 kHz x 680 PF

'VOUT = 1.9 x 0.01:2 + =19 mV

§8 x x COUT

fSW

'VOUT = IPP x RESR2 + [V]

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

8.3.15 VCC Capacitor CVCC

The primary purpose of the VCC capacitor (CVCC) is to supply the peak transient currents of the LO driver and

bootstrap diode as well as provide stability for the VCC regulator. These peak currents can be several amperes.

The recommended value of CVCC should be no smaller than 0.47μF, and should be a good quality, low ESR,

ceramic capacitor. CVCC should be placed at the pins of the IC to minimize potentially damaging voltage

transients caused by trace inductance. A value of 1μF was selected for this design.

8.3.16 Output Capacitor CO

The output capacitors smooth the output voltage ripple caused by inductor ripple current and provide a source of

charge during transient loading conditions. For this design example, a 680μF electrolytic capacitor with maximum

10mΩESR was selected as the main output capacitor. The fundamental component of the output ripple voltage

with maximum ESR is approximated as:

(43)

(44)

Additional low ERS / ESL ceramic capacitors can be placed in parallel with the main output capacitor to further

reduce the output voltage ripple and spikes. In this example, two 22μF capacitors were added.

8.3.17 Input Capacitor CIN

The regulator input supply voltage typically has high source impedance at the switching frequency. Good quality

input capacitors are necessary to limit the ripple voltage at the VIN pin while supplying most of the switch current

during the on-time. When the high-side NMOS device turns on, the current into the device steps to the valley of

the inductor current waveform, ramps up to the peak value, and then drops to the zero at turnoff. The input

capacitor should be selected for RMS current rating and minimum ripple voltage. A good approximation for the

required ripple current rating necessary is IRMS > IOUT / 2.

In this example, seven 2.2μF ceramic capacitors were used. With ceramic capacitors, the input ripple voltage will

be triangular. The input ripple voltage can be approximated as:

(45)

(46)

Capacitors connected in parallel should be evaluated for RMS current rating. The current will split between the

input capacitors based on the relative impedance of the capacitors at the switching frequency.

8.3.18 VIN Filter RVIN, CVIN

An R-C filter (RVIN, CVIN) on VIN is optional. The filter helps to prevent faults caused by high frequency switching

noise injection into the VIN pin. 0.47μF ceramic capacitor is used for CVIN in the example.

8.3.19 Soft-Start Capacitor CSS

The capacitor at the SS pin (CSS) determines the soft-start time (tSS), which is the time for the output voltage to

reach the final regulated value. The tSS for a given CSS can be calculated from Equation 8 as follows:

(47)

For this example, a value of 0.047μF was chosen for a soft-start time of 3.8ms.

Product Folder Links: LM25117 LM25117-Q1

CHF 5 m: x 724 µF x 10 nF

27.4 k: x 10 nF - 5 m: x 724 µF

== 134 pF

CHF RESR x COUT x CCOMP

RCOMP x CCOMP - RESR x COUT

=[F]

CCOMP 27.4 k:

=x 724 µF

3.3V

9A = 10 nF

CCOMP RLOAD x COUT

RCOMP

=[F]

RCOMP = 2Sx 8 m: x 10 x 724 µF x 3.24 k: x 23 kHz = 27.1 k:

RCOMP = 2Sx RS x AS x COUT x RFB2 x fCROSS [:@

fCROSS = = 23 kHz

fSW

RFB2 - 1

RFB1 VOUT

0.8V

0.47 µF x 1.25V

10 µA= 59 ms

tRES =

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

8.3.20 Restart Capacitor CRES

The capacitor at the RES pin (CRES) determines tRES, which is the time the LM25117 remains off before a restart

attempt is made in hiccup mode current limiting. tRES for a given CRES can be calculated from Equation 13 as

follows:

(48)

For this example, a value of 0.47μF was chosen for a restart time of 59ms.

8.3.21 Output Voltage Divider RFB2 and RFB1

RFB1 and RFB2 set the output voltage level. The ratio of these resistors is calculated as:

(49)

The ratio between RCOMP and RFB2 determines the mid-band gain, AFB_MID. A larger value for RFB2 may require a

corresponding larger value for RCOMP. RFB2 should be large enough to keep the total divider power dissipation

small. 3.24kΩwas chosen for RFB2 in this example, which results in a RFB1 value of 1.05kΩfor 3.3V output.

8.3.22 Loop Compensation Components CCOMP, RCOMP and CHF

RCOMP, CCOMP and CHF configure the error amplifier gain and phase characteristics to produce a stable voltage

loop. For a quick start, follow the 4 steps listed below.

STEP1: Select fCROSS

By selecting one tenth of the switching frequency, fCROSS is calculated as follows:

(50)

STEP2: Determine required RCOMP

Knowing fCROSS, RCOMP is calculated as follows:

(51)

(52)

The standard value of 27.4kΩwas selected for RCOMP

STEP3: Determine CCOMP to cancel load pole

Knowing RCOMP, CCOMP is calculated as follows:

(53)

(54)

The standard value of 10nF was selected for CCOMP

STEP4: Determine CHF to cancel ESR zero

Knowing RCOMP and CCOMP, CHF is calculated as follows:

(55)

(56)

Half of the maximum ESR is assumed as a typical ESR. The standard value of 150pF was selected for CHF.

Product Folder Links: LM25117 LM25117-Q1

ZP_EA = RCOMP x CHF

ZP_EA = RCOMP x (CHF // CCOMP

)

ZZ_EA =RCOMP x CCOMP

AFB_MID = RCOMP

RFB2

AFB_MID = RCOMP

RFB2

AFB = 1

RFB2 x (CCOMP + CHF)

AFB = 1

RFB2 x (CCOMP + CHF)

AFB x

ZP_EA

VOUT

VCOMP

-ZZ_EA

1 +

s x (1+ )

AFB x

ZP_EA

VOUT

VCOMP

-ZZ_EA

1 +

s x (1+ )

K = 1

K = LO

RRAMP x CRAMP x RS x AS

fSW

Zn = ZSW

2=Sx fSW or fn =

Q = 1

S(K - 0.5)

ZP_HF Q x Zn

ZP_HF fSW

K  0.5

= or

ZP_LF = RLOAD x COUT

ZP_LF = (RLOAD + RESR1) x (COUT1 + COUT2)LO x (COUT1 + COUT2) x ZP_HF

1 1

RESR1

ZP_ESR = x (COUT1 // COUT2

)

ZZ_ESR = RESR

x COUT

ZZ_ESR = RESR1

x COUT1

AM = RLOAD

RS x AS x LO

ZP_HF

x 1

1 +

RLOAD

AM = RLOAD

RS x AS

(1 + )

ZZ_ESR

VOUT

VCOMP

^AM x

ZP_LF

1 +

VOUT

VCOMP

^AM x ZZ_ESR

1 +

(1 + )

ZP_LF x(1 + )

ZP_ESR x(1 + + )

ZP_HF s2

Zn2

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

Table 1. LM25117 Frequency Analysis Formulas

SIMPLE FORMULA COMPREHENSIVE FORMULA(1)

Modulator

Transfer

Function

Modulator DC

Gain

ESR Zero

ESR Pole Not considered

Dominant Load

Pole

Sampled Gain Not considered

Inductor Pole

Quality Factor Not considered

Sub-harmonic Not considered

Double Pole

K Factor

Feedback

Transfer

Function

Feedback DC

Gain

Mid-band Gain

Low Frequency

Zero

High Frequency

Pole

(1) Comprehensive Equation includes an inductor pole and a gain peaking at fSW/2, which caused by sampling effect of the current mode

control. Also it assumes that a ceramic capacitor COUT2 (No ESR) is connected in parallel with COUT1. RESR1 represents ESR of COUT1 .

Product Folder Links: LM25117 LM25117-Q1

fCROSS_MAX = fSW

4 x Q 1 + 4 x Q2-1

x ( )

ZP_EA = ZZ_ESR

ZZ_EA = ZP_LF

when &

fCROSS < ZP_HF

2 x S x 10

& & fCROSS < ZP_ESR

2 x S x 10

ZP_EA = ZZ_ESR

ZZ_EA = ZP_LF &

when

2 x ' x RS x RFB2 x AS x COUT

RCOMP

fCROSS =

2 x ' x RS x RFB2 x AS x (COUT1 + COUT2)

RCOMP

fCROSS =

ZZ_EA = ZP_LF

when

ZP_EA = ZZ_ESR

ZZ_EA = ZP_LF &

when

T(s) = s

AM x AFB xZZ_ESR

1 +

(1 + )

ZP_EA x(1 + )

ZP_ESR x(1 + + )

ZP_HF s2

Zn2

T(s) AM x AFB

T(s) = AM x AFB x ZZ_EA

(1 + )

ZP_EA

1 +

s x

(1 + )

ZP_LF

ZZ_ESR

1 +

T(s) = AM x AFB x x

ZZ_ESR

1 +

(1 + )

ZP_LF x(1 + )

ZP_ESR x(1 + + )

ZP_HF s2

Zn2s

(1 + )

ZP_EA

s x

ZZ_EA

1 +

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

Table 1. LM25117 Frequency Analysis Formulas (continued)

SIMPLE FORMULA COMPREHENSIVE FORMULA(1)

Open-Loop

Response

Crossover

Frequency

(Open Loop

Bandwidth)

Maximum

Crossover

Frequency The frequency at which 45° phase shift occurs in modulator phase

characteristics.

8.4 Application Curves

Figure 34. Typical Efficiency vs Load Current

Figure 33. Start-Up with Resistive Load

Product Folder Links: LM25117 LM25117-Q1

VOUT

RES

COMP

RAMP

PGND

CSG

VCC

VIN

AGND

UVLO

VCCDIS

DEMB

VIN

VOUT

LM25117

CIN

CHB

DHB

CVCC

Hiccup Mode OVP

Triggered at 13.4V

CC Mode: 2A

100k:

15 k:

80 µF

68 µH

1500 pF

100 k:

22.1 k:0.47 µF

3.24 k:

2.37 k:

0.022 µF

47 m:

Current Control (CC)

3.24 k:

332:

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

Application Curves (continued)

8.4.1 Constant Current Regulator

The LM25117 can be configured as a constant current regulator by using the current monitor feature (CM) as the

feedback input. A voltage divider at the VCCDIS pin from VOUT to AGND can be used to protect against output

over-voltage. When the VCCDIS pin voltage is greater than the VCCDIS threshold, the controller disables the

VCC regulator and the VCC pin voltage decays. When the VCC pin voltage is less than the VCC UV threshold,

both HO and LO outputs stop switching. Due to the time delay required for VCC to decay below the VCC UV

threshold, the over-voltage protection operates in hiccup mode. See Figure 35.

Figure 35. Constant Current Regulator with Hiccup Mode Output OVP

8.4.2 Constant Voltage and Constant Current Regulator

The LM25117 also can be configured as a constant voltage and constant current regulator, known as CV+CC

regulator. In this configuration, there is much less variation in the current limiting as compared to peak cycle-by-

cycle current limiting of the inductor current. The LMV431 and the PNP transistor create a voltage-to-current

amplifier in the current loop. This amplifier circuitry does not affect the normal operation when the output current

is less than the current limit set-point. When the output current is greater than the set-point, the PNP transistor

sources a current into CRAMP and increases the positive slope of emulated inductor current ramp until the output

current is less than or equal to the current limit set-point. See Figure 36 and Figure 37.

Product Folder Links: LM25117 LM25117-Q1

VOUT

RES

COMP

RAMP

PGND

CSG

VCC

VIN

AGND

UVLO

VCCDIS

DEMB

VIN

VOUT

LM25117

CIN

Current Control (CC)

CHB

DHB

CVCC

VCC

Voltage Control (CV)

LMV431

CV Mode : 5V

CC Mode: 2A

100 k:

15 k:

80 PF

68 PH

1500 pF

100 k:

22.1 k:0.33 PF x2

3.24 k:

619:

34.8 k:0.1 PF

47 m:

1 nF

100 k:

10 k:100:

PNP

200 k:

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

Application Curves (continued)

Figure 36. Constant Voltage Regulator with Accurate Current Limit

Figure 37. Current Limit Comparison

Product Folder Links: LM25117 LM25117-Q1

Controller

VOUTGNDGNDVIN

Inductor

CIN

COUT

RSENSE

Place controller as

close to the switches

LM25117

LM25117-Q1

www.ti.com

SNVS714F –APRIL 2011–REVISED AUGUST 2015

9 Power Supply Recommendations

LM25117 is a power management device. The power supply for the device is any DC voltage source within the

specified input range.

10 Layout

10.1 Layout Guideline

Figure 38. Layout Example

10.1.1 PC Board Layout Recommendations

In a buck regulator the primary switching loop consists of the input capacitor, NMOS power switches and current

sense resistor. Minimizing the area of this loop reduces the stray inductance and minimizes noise and possible

erratic operation. High quality input capacitors should be placed as close as possible to the NMOS power

switches, with the VIN side of the capacitor connected directly to the high-side NMOS drain and the ground side

of the capacitor connected as close as possible to the current sense resistor ground connection.

Connect all of the low power ground connections (RUV1, RT, RFB1, CSS, CRES, CCM, CVIN, CRAMP) directly to the

regulator AGND pin. Connect CVCC directly to the regulator PGND pin. Note that CVIN and CVCC must be as

physically close as possible to the IC. AGND and PGND must be directly connected together through a top-side

copper pattern connected to the exposed pad. Ensure no high current flows beneath the underside exposed pad.

The LM25117 has an exposed thermal pad to aid power dissipation. Adding several vias under the exposed pad

helps conduct heat away from the IC. The junction to ambient thermal resistance varies with application. The

most significant variables are the area of copper in the PC board, the number of vias under the exposed pad and

the amount of forced air cooling. The integrity of the solder connection from the IC exposed pad to the PC board

is critical. Excessive voids greatly decrease the thermal dissipation capacity.

The highest power dissipating components are the two power switches. Selecting NMOS switches with exposed

pads aids the power dissipation of these devices.

Product Folder Links: LM25117 LM25117-Q1

LM25117

LM25117-Q1

SNVS714F –APRIL 2011–REVISED AUGUST 2015

www.ti.com

11 Device and Documentation Support

11.1 Community Resources

The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective

contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of

Use.

TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration

among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help

solve problems with fellow engineers.

Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and

contact information for technical support.

11.2 Related Links

The table below lists quick access links. Categories include technical documents, support and community

resources, tools and software, and quick access to sample or buy.

Table 2. Related Links

TECHNICAL TOOLS & SUPPORT &

PARTS PRODUCT FOLDER SAMPLE & BUY DOCUMENTS SOFTWARE COMMUNITY

LM25117 Click here Click here Click here Click here Click here

LM25117-Q1 Click here Click here Click here Click here Click here

11.3 Trademarks

E2E is a trademark of Texas Instruments.

All other trademarks are the property of their respective owners.

11.4 Electrostatic Discharge Caution

These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

11.5 Glossary

SLYZ022 —TI Glossary.

This glossary lists and explains terms, acronyms, and definitions.

12 Mechanical, Packaging, and Orderable Information

The following pages include mechanical, packaging, and orderable information. This information is the most

current data available for the designated devices. This data is subject to change without notice and revision of

this document. For browser-based versions of this data sheet, refer to the left-hand navigation.

Product Folder Links: LM25117 LM25117-Q1

PACKAGE OPTION ADDENDUM

www.ti.com 10-Dec-2020

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead finish/

Ball material

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

LM25117PMH/NOPB ACTIVE HTSSOP PWP 20 73 RoHS & Green SN Level-3-260C-168 HR -40 to 125 LM25117

PMH

LM25117PMHE/NOPB ACTIVE HTSSOP PWP 20 250 RoHS & Green SN Level-3-260C-168 HR -40 to 125 LM25117

PMH

LM25117PMHX/NOPB ACTIVE HTSSOP PWP 20 2500 RoHS & Green SN Level-3-260C-168 HR -40 to 125 LM25117

PMH

LM25117PSQ/NOPB ACTIVE WQFN RTW 24 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 L25117P

LM25117PSQE/NOPB ACTIVE WQFN RTW 24 250 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 L25117P

LM25117PSQX/NOPB ACTIVE WQFN RTW 24 4500 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 L25117P

LM25117QPMH/NOPB ACTIVE HTSSOP PWP 20 73 RoHS & Green SN Level-3-260C-168 HR -40 to 125 LM25117

QPMH

LM25117QPMHE/NOPB ACTIVE HTSSOP PWP 20 250 RoHS & Green SN Level-3-260C-168 HR -40 to 125 LM25117

QPMH

LM25117QPMHX/NOPB ACTIVE HTSSOP PWP 20 2500 RoHS & Green SN Level-3-260C-168 HR -40 to 125 LM25117

QPMH

LM25117QPSQ/NOPB ACTIVE WQFN RTW 24 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 L25117Q

LM25117QPSQE/NOPB ACTIVE WQFN RTW 24 250 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 L25117Q

LM25117QPSQX/NOPB ACTIVE WQFN RTW 24 4500 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 L25117Q

(1) The marketing status values are defined as follows:

ACTIVE: Product device recommended for new designs.

LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.

NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.

PREVIEW: Device has been announced but is not in production. Samples may or may not be available.

OBSOLETE: TI has discontinued the production of the device.

(2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance

do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may

reference these types of products as "Pb-Free".

RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.

PACKAGE OPTION ADDENDUM

www.ti.com 10-Dec-2020

Addendum-Page 2

Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based

flame retardants must also meet the <=1000ppm threshold requirement.

(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.

(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation

of the previous line and the two combined represent the entire Device Marking for that device.

(6) Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two

lines if the finish value exceeds the maximum column width.

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information

provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and

continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.

TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.

In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.

OTHER QUALIFIED VERSIONS OF LM25117, LM25117-Q1 :

•Catalog: LM25117

•Automotive: LM25117-Q1

NOTE: Qualified Version Definitions:

•Catalog - TI's standard catalog product

•Automotive - Q100 devices qualified for high-reliability automotive applications targeting zero defects

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device Package

Type Package

Drawing Pins SPQ Reel

Diameter

(mm)

Reel

Width

W1 (mm)

(mm) B0

(mm) K0

(mm) P1

(mm) W

(mm) Pin1

Quadrant

LM25117PMHE/NOPB HTSSOP PWP 20 250 178.0 16.4 6.95 7.1 1.6 8.0 16.0 Q1

LM25117PMHX/NOPB HTSSOP PWP 20 2500 330.0 16.4 6.95 7.1 1.6 8.0 16.0 Q1

LM25117PSQ/NOPB WQFN RTW 24 1000 178.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1

LM25117PSQE/NOPB WQFN RTW 24 250 178.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1

LM25117PSQX/NOPB WQFN RTW 24 4500 330.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1

LM25117QPMHE/NOPB HTSSOP PWP 20 250 178.0 16.4 6.95 7.1 1.6 8.0 16.0 Q1

LM25117QPMHX/NOPB HTSSOP PWP 20 2500 330.0 16.4 6.95 7.1 1.6 8.0 16.0 Q1

LM25117QPSQ/NOPB WQFN RTW 24 1000 178.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1

LM25117QPSQE/NOPB WQFN RTW 24 250 178.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1

LM25117QPSQX/NOPB WQFN RTW 24 4500 330.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1

PACKAGE MATERIALS INFORMATION

www.ti.com 20-Sep-2016

Pack Materials-Page 1

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)

LM25117PMHE/NOPB HTSSOP PWP 20 250 210.0 185.0 35.0

LM25117PMHX/NOPB HTSSOP PWP 20 2500 367.0 367.0 38.0

LM25117PSQ/NOPB WQFN RTW 24 1000 210.0 185.0 35.0

LM25117PSQE/NOPB WQFN RTW 24 250 210.0 185.0 35.0

LM25117PSQX/NOPB WQFN RTW 24 4500 367.0 367.0 35.0

LM25117QPMHE/NOPB HTSSOP PWP 20 250 210.0 185.0 35.0

LM25117QPMHX/NOPB HTSSOP PWP 20 2500 367.0 367.0 38.0

LM25117QPSQ/NOPB WQFN RTW 24 1000 210.0 185.0 35.0

LM25117QPSQE/NOPB WQFN RTW 24 250 210.0 185.0 35.0

LM25117QPSQX/NOPB WQFN RTW 24 4500 367.0 367.0 35.0

PACKAGE MATERIALS INFORMATION

www.ti.com 20-Sep-2016

Pack Materials-Page 2

MECHANICAL DATA

PWP0020A

www.ti.com

MXA20A (Rev C)

IMPORTANT NOTICE AND DISCLAIMER

TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATASHEETS), DESIGN RESOURCES (INCLUDING REFERENCE

DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS”

AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY

IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD

PARTY INTELLECTUAL PROPERTY RIGHTS.

These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate

TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable

standards, and any other safety, security, or other requirements. These resources are subject to change without notice. TI grants you

permission to use these resources only for development of an application that uses the TI products described in the resource. Other

reproduction and display of these resources is prohibited. No license is granted to any other TI intellectual property right or to any third

party intellectual property right. TI disclaims responsibility for, and you will fully indemnify TI and its representatives against, any claims,

damages, costs, losses, and liabilities arising out of your use of these resources.

TI’s products are provided subject to TI’s Terms of Sale (www.ti.com/legal/termsofsale.html) or other applicable terms available either on

ti.com or provided in conjunction with such TI products. TI’s provision of these resources does not expand or otherwise alter TI’s applicable

warranties or warranty disclaimers for TI products.

Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265