General Description
The MAX17503/MAX17503S high-efficiency, high-
voltage, synchro nously rectified step-down converter with
dual integrated MOSFETs operates over a 4.5V to 60V
input. It delivers up to 2.5A and 0.9V to 90%VIN output
voltage. Built-in compensation across the output voltage
range eliminates the need for external components. The
feedback (FB) regulation accuracy over -40°C to +125°C
is ±1.1%. The device is available in a compact (4mm x
4mm) TQFN lead(Pb)-free package with an exposed pad.
Simulation models are available.
The device features a peak-current-mode control
architecture with a MODE feature that can be used to
operate the device in pulse-width modulation (PWM),
pulse-frequency modulation (PFM), or discontinuous-
conduction mode (DCM) control schemes. PWM operation
provides constant frequency operation at all loads, and is
useful in applications sensitive to switching frequency.
PFM operation disables negative inductor current and
additionally skips pulses at light loads for high efficiency.
DCM features constant frequency operation down to
lighter loads than PFM mode by not skipping pulses, but
only disabling negative inductor current at light loads.
DCM operation offers efficiency performance that lies
between PWM and PFM modes. The MAX17503S offers
a lower minimum on-time that allows for higher switching
frequencies and a smaller solution size.
A programmable soft-start feature allows users to reduce
input inrush current. The device also incorporates an
output enable/undervoltage lockout pin (EN/UVLO) that
allows the user to turn on the part at the desired input-
voltage level. An open-drain RESET pin provides a
delayed power-good signal to the sys tem upon achieving
successful regulation of the output voltage.
Applications
●Industrial Power Supplies
●Distributed Supply Regulation
●Base Station Power Supplies
●Wall Transformer Regulation
●High-Voltage Single-Board Systems
●General-Purpose Point-of-Load
Benets and Features
●Eliminates External Components and Reduces
Total Cost
• No Schottky-Synchronous Operation for High
E󰀩ciency and Reduced Cost
• Internal Compensation for Stable Operation at Any
Output Voltage
• All-Ceramic Capacitor Solution: Ultra-Compact
Layout with as Few as Eight External Components
●Reduces Number of DC-DC Regulators to Stock
• Wide 4.5V to 60V Input Voltage Range
• 0.9V to 90%VIN Output Voltage
• Delivers up to 2.5A Over Temperature
• 100kHz to 2.2MHz Adjustable Frequency with
External Synchronization
• MAX17503S Allows Higher Frequency of Operation
• Available in a 20-Pin, 4mm x 4mm TQFN Package
●Reduces Power Dissipation
• Peak E󰀩ciency > 90%
• PFM and DCM Modes for High Light-Load E󰀩ciency
• Shutdown Current = 2.µ8µA (typ)
●Operates Reliably
• Hiccup-Mode Current Limit and Autoretry Startup
• Built-In Output-Voltage Monitoring (Open-Drain
RESET Pin)
• Resistor-Programmable EN/UVLO Threshold
• Adjustable Soft-Start and Prebiased Power-Up
• High Industrial -40°C to +125°C Ambient Operating
Temperature Range/-40°C to +150°C Junction
Temperature Range
19-6669; Rev 3; 4/17
Ordering Information appears at end of data sheet.
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
EVALUATION KIT AVAILABLE
VIN to PGND .........................................................-0.3V to +65V
EN/UVLO to SGND ...............................................-0.3V to +65V
LX to PGND................................................-0.3V to (VIN + 0.3V)
BST to PGND ........................................................-0.3V to +70V
BST to LX .............................................................-0.3V to +6.5V
BST to VCC ...........................................................-0.3V to +65V
CF, RESET, SS, MODE, SYNC,
RT to SGND .....................................................-0.3V to +6.5V
FB to SGND .........................................................-0.3V to +1.5V
VCC to SGND .......................................................-0.3V to +6.5V
SGND to PGND ....................................................-0.3V to +0.3V
LX Total RMS Current ...........................................................±4A
Output Short-Circuit Duration .................................... Continuous
Continuous Power Dissipation (TA = +70ºC) (multilayer board)
TQFN (derate 30.3mW/ºC above TA = +70ºC) ......2424.2mW
Junction Temperature ...................................................... +150ºC
Storage Temperature Range .............................-65NC to +160ºC
Lead Temperature (soldering, 10s) ................................. +300ºC
Soldering Temperature (reflow) ....................................... +260ºC
(VIN = VEN/UVLO = 24V, RRT = 40.2kI (500kHz), CVCC = 2.2μF, VPGND = VSGND = VMODE = VSYNC = 0V, LX = SS = RESET =
open, VBST to VLX = 5V, VFB = 1V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are
referenced to SGND, unless otherwise noted.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
INPUT SUPPLY (VIN)
Input Voltage Range VIN 4.5 60 V
Input Shutdown Current IIN-SH VEN/UVLO = 0V (shutdown mode) 2.8 4.5
µA
Input Quiescent Current
IQ_PFM
VFB = 1V, MODE = RT = open 118
VFB = 1V, MODE = open 162
IQ-DCM DCM mode, VLX = 0.1V 1.16 1.8
mA
IQ_PWM
Normal switching mode, fSW = 500kHz, VFB
= 0.8V 9.5
Maxim Integrated
│
2
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Electrical Characteristics
Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer board.
For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial.
Note 1: Junction temperature greater than +125°C degrades operating lifetimes.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only; functional operation of the device at these or any
other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device
reliability.
Absolute Maximum Ratings (Note 1)
Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
PACKAGE TYPE: 20 TQFN
Package Code T2044+4
Outline Number 21-0139
Land Pattern Number 90-0409
THERMAL RESISTANCE, FOUR-LAYER BOARD
Junction to Ambient (θJA) 33°C/W
Junction to Case (θJC) 2°C/W
(VIN = VEN/UVLO = 24V, RRT = 40.2kI (500kHz), CVCC = 2.2μF, VPGND = VSGND = VMODE = VSYNC = 0V, LX = SS = RESET =
open, VBST to VLX = 5V, VFB = 1V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are
referenced to SGND, unless otherwise noted.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
ENABLE/UVLO (EN/UVLO)
EN/UVLO Threshold VENR VEN/UVLO rising 1.19 1.215 1.26 V
VENF VEN/UVLO falling 1.068 1.09 1.131
EN/UVLO Input Leakage Current IEN VEN/UVLO = 0V, TA = +25ºC -50 0 +50 nA
LDO
VCC Output Voltage Range VCC
6V < VIN < 60V, IVCC = 1mA 4.75 5 5.25 V
1mA ≤ IVCC ≤ 25mA
VCC Current Limit IVCC-MAX VCC = 4.3V, VIN = 6V 26.5 54 100 mA
VCC Dropout VCC-DO VIN = 4.5V, IVCC = 20mA 4.2 V
VCC UVLO VCC_UVR VCC rising 4.05 4.2 4.3 V
VCC_UVF VCC falling 3.65 3.8 3.9
POWER MOSFET AND BST DRIVER
High-Side nMOS On-Resistance RDS-ONH ILX = 0.3A 165 325 mI
Low-Side nMOS On-Resistance RDS-ONL ILX = 0.3A 80 150 mI
LX Leakage Current ILX_LKG VLX = VIN - 1V, VLX = VPGND + 1V, TA = +25ºC -2 +2 µA
SOFT-START (SS)
Charging Current ISS VSS = 0.5V 4.7 5 5.3 µA
FEEDBACK (FB)
FB Regulation Voltage VFB_REG -40ºC ≤ TA ≤ +125ºC 0.89 0.9 0.91 V
FB Input Bias Current IFB 0 < VFB < 1V, TA = +25ºC -50 +50 nA
MODE
MODE Threshold
VM-DCM MODE = VCC (DCM mode) VCC -
1.6
V
VM-PFM MODE = open (PFM mode) VCC / 2
VM-PWM MODE = GND (PWM mode) 1.4
PFM/HIBERNATE MODE
FB Threshold for Entering
Hibernate Mode VFB_HBR VFB rising 100.8 102.3 103.5 %
FB Threshold for Exiting Hibernate
Mode VFB_HBF VFB falling 100 101.1 102.3 %
CURRENT LIMIT
Peak Current-Limit Threshold IPEAK-LIMIT 3.2 3.7 4.3 A
Runaway Current-Limit Threshold IRUNAWAY-LIMIT 3.7 4.3 5 A
Valley Current-Limit Threshold ISINK-LIMIT
MODE = open/VCC -0.16 0 +0.16 A
MODE = GND -1.8
PFM Current-Limit Threshold IPFM MODE = open 0.6 0.75 0.9 A
Maxim Integrated
│
3
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Electrical Characteristics (continued)
(VIN = VEN/UVLO = 24V, RRT = 40.2kI (500kHz), CVCC = 2.2μF, VPGND = VSGND = VMODE = VSYNC = 0V, LX = SS = RESET =
open, VBST to VLX = 5V, VFB = 1V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are
referenced to SGND, unless otherwise noted.) (Note 2)
Note 2: All limits are 100% tested at +25ºC. Limits over temperature are guaranteed by design.
Note 3: See the Overcurrent Protection/Hiccup Mode Section for more details.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
RT AND SYNC
Switching Frequency fSW
RRT = 210kΩ90 100 110
kHz
RRT = 102kΩ 180 200 220
RRT = 40.2kΩ 475 500 525
RRT = 8.06kΩ 1950 2200 2450
RRT = open 460 500 540
SYNC Frequency Capture Range fSW set by RRT
1.1 x
fSW
1.4 x
fSW
kHz
SYNC Pulse Width 50 ns
SYNC Threshold VIH 2.1 V
VIL 0.8
FB Undervoltage Trip Level to
Cause Hiccup VFB-HICF 0.56 0.58 0.65 V
Hiccup Timeout (Note 3) 32,768 Cycles
Minimum On-Time tON-MIN
MAX17503 135 ns
MAX17503S 55 80 ns
Minimum O󰀨-Time tOFF-MIN 140 160 ns
LX Dead Time 5 ns
RESET
RESET Output Level Low IRESET = 10mA 0.4 V
RESET Output Leakage Current TA = TJ = +25ºC, VRESET = 5.5V -0.1 +0.1 µA
FB Threshold for RESET Assertion VFB-OKF VFB falling 90.5 92 94.6 %VFB-
REG
FB Threshold for RESET
Deassertion VFB-OKR VFB rising 93.8 95 97.8 %VFB-
REG
RESET Deassertion Delay After FB
Reaches 95% Regulation 1024 Cycles
THERMAL SHUTDOWN
Thermal-Shutdown Threshold Temperature rising 165 ºC
Thermal-Shutdown Hysteresis 10 ºC
Maxim Integrated
│
4
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Electrical Characteristics (continued)
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS = 5600pF, RT = MODE = open, TA = -40°C to
+125°C, unless otherwise noted. Typical values are at TA = +25ºC. All voltages are referenced to GND, unless otherwise noted.)
MAX17503, 5V OUTPUT, PWM MODE, FIGURE 4a
CIRCUIT EFFICIENCY vs. LOAD CURRENT
MAX17503 toc01
EFFICIENCY (%)
200015001000500
50
60
70
80
90
100
40
0
2500
VIN = 12V VIN = 48V
MODE = SGND
VIN = 24V VIN = 36V
LOAD CURRENT (mA)
30
40
50
60
70
80
90
100
0500 1000 1500 2000 2500
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17503S, 5V OUTPUT, PWM MODE,
FIGURE 4cCIRCUIT,
EFFICIENCY vs. L OAD CURRENT
V
IN
= 48V
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
MODE = SGND
toc01a
MAX17503, 3.3V OUTPUT, PWM MODE, FIGURE 4b
CIRCUIT EFFICIENCY vs. LOAD CURRENT
MAX17503 toc02
EFFICIENCY (%)
200015001000500
50
60
70
80
90
100
40
02500
VIN = 12V
VIN = 48V
MODE = SGND
VIN = 24V VIN = 36V
LOAD CURRENT (mA)
MAX17503, 5V OUTPUT, PFM MODE, FIGURE 4a
CIRCUIT EFFICIENCY vs. LOAD CURRENT
MAX17503 toc03
LOAD CURRENT (mA)
EFFICIENCY (%)
100010010
65
70
75
80
85
90
95
100
60
1 2500
VIN = 12V
VIN = 48V
VIN = 24V
VIN = 36V
MODE = OPEN
30
40
50
60
70
80
90
100
10 100 1000
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17503S, 5V OUTPUT,
PFM MODE, FIGURE 4cCIRCUIT,
EFFICIENCY vs. L OAD CURRENT
V
IN
= 48V
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
MODE = OPEN
2500
toc03a
20
30
40
50
60
70
80
90
100
0500 1000 1500 2000 2500
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17503S, 3.3V OUTPUT,
PWM MODE, FIGURE 4d CIRCUIT,
EFFICIENCY vs. L OAD CURRENT
V
IN
= 48V
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
MODE = SGND
toc02a
MAX17503, 3.3V OUTPUT, PFM MODE, FIGURE 4b
CIRCUIT EFFICIENCY vs. LOAD CURRENT
MAX17503 toc04
LOAD CURRENT (mA)
EFFICIENCY (%)
100010010
60
65
70
75
80
85
90
95
100
50
55
1 2500
VIN = 12V
VIN = 48V
VIN = 24V
VIN = 36V
MODE = OPEN
30
40
50
60
70
80
90
100
10 100 1000
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17503S, 3.3V OUTPUT,
PFM MODE, FIGURE 4d CIRCUIT,
EFFICIENCY v s . LOAD CURRENT
V
IN
= 48V
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
MODE = OPEN
toc04a
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
5
www.maximintegrated.com
Typical Operating Characteristics
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS = 5600pF, RT = MODE = open, TA = -40°C to
+125°C, unless otherwise noted. Typical values are at TA = +25ºC. All voltages are referenced to GND, unless otherwise noted.)
3.10
3.15
3.20
3.25
3.30
3.35
3.40
3.45
3.50
0500 1000 1500 2000 2500
OUTPUT VOLTAGE (V)
LOAD CURRENT (mA)
MAX17503S, 3.3V OUTPUT,
PWM MODE, FIGURE 4d CIRCUIT,
LOAD AND L INE REGULATION
V
IN
= 36V
V
IN
= 48V
V
IN
= 24V
V
IN
= 12V
toc08a
MAX17503 5V OUTPUT, DCM MODE, FIGURE 4a
CIRCUIT EFFICIENCY vs. LOAD CURRENT
MAX17503 toc05
LOAD CURRENT (mA)
EFFICIENCY (%)
100010010
30
40
50
60
70
80
90
100
20
1 2500
VIN = 12V
VIN = 48V
VIN = 24V
VIN = 36V
MODE = VCC
MAX17503, 3.3V OUTPUT, DCM MODE, FIGURE 4b
CIRCUIT EFFICIENCY vs. LOAD CURRENT
MAX17503 toc06
LOAD CURRENT (mA)
EFFICIENCY (%)
1000100101 2500
VIN = 12V
VIN = 48V
VIN = 24V
VIN = 36V
MODE = VCC
30
40
50
60
70
80
90
100
20
MAX17503, 5V OUTPUT, PWM MODE, FIGURE 4a
CIRCUIT LOAD AND LINE REGULATION
MAX17503 toc07
OUTPUT VOLTAGE (V)
4.96
4.97
4.98
4.99
5.00
5.01
5.02
5.03
5.04
5.05
4.95
200015001000500
02500
VIN = 12V VIN = 24V VIN = 36V
VIN = 48V
LOAD CURRENT (mA)
MODE = SGND
MAX17503,
3.3V OUTPUT, PWM MODE, FIGURE 4b
CIRCUIT LOAD AND LINE REGULATION
MAX17503 toc08
OUTPUT VOLTAGE (V)
3.26
3.27
3.28
3.29
3.30
3.31
3.32
3.33
3.34
3.35
3.25
200015001000500
02500
VIN = 12V VIN = 24V VIN = 36V
VIN = 48V
LOAD CURRENT (mA)
MODE = SGND
0
10
20
30
40
50
60
70
80
90
100
110 100 1000
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17503S, 5V OUTPUT,
DCM MODE, FIGURE 4cCIRCUIT,
EFFICIENCY vs. L OAD CURRENT
V
IN
= 48V
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
MODE = VCC
toc05a
4.92
4.93
4.94
4.95
4.96
4.97
4.98
4.99
5.00
5.01
5.02
0500 1000 1500 2000 2500
OUTPUT VOLTAGE (V)
LOAD CURRENT (mA)
MAX17503S, 5V OUTPUT,
PWM MODE, FIGURE 4c CIRCUIT,
LOAD AND LINE REGULATION
V
IN
= 36V
V
IN
= 48V
V
IN
= 24V
V
IN
= 12V
toc07a
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
6
www.maximintegrated.com
10
20
30
40
50
60
70
80
90
100
110 100 1000
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17503S, 3.3V OUTPUT,
DCM MODE, FIGURE 4dCIRCUIT,
EFFICIENCY vs. L OAD CURRENT
V
IN
= 48V
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
MODE = VCC
toc06a
Typical Operating Characteristics (continued)
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS = 5600pF, RT = MODE = open, TA = -40°C to
+125°C, unless otherwise noted. Typical values are at TA = +25ºC. All voltages are referenced to GND, unless otherwise noted.)
MAX17503, 3.3V OUTPUT, PFM MODE, FIGURE 4b
CIRCUIT
LOAD AND LINE REGULATION
MAX17503 toc10
OUTPUT VOLTAGE (V)
3.2
3.1
3.3
3.4
3.5
3.6
3.0
VIN = 36V
200015001000500
0
2500
VIN = 12V
LOAD CURRENT (mA)
MODE = OPEN
VIN = 48V
VIN = 24V
SWITCHING FREQUENCY vs.
RT RESISTANCE
MAX17503 toc11
RRT (kΩ)
SWITCHING FREQUENCY (kHz)
908060 7020 30 40 5010
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
0
0 100
MAX17503,
SOFT-START/SHUTDOWN FROM EN/UVLO
5V OUTPUT, 2.5A LOAD CURRENT,
FIGURE 4a CIRCUIT
MAX17503 toc12
VRESET
5V/div
IOUT
1A/div
VOUT
2V/div
VEN/UVLO
2V/div
1ms/div
1A/div
1ms/div
V
EN/UVLO
5V/div
MAX17503S, SOFT-START/
SHUTDOWN FROM EN/UVL O, 5V OUTPUT,
2.5A L OAD CURRENT, FIGURE 4cCIRCUIT)
V
OUT
I
OUT
2V/div
5V/div
V
RESET
toc12a
MAX17503, 5V OUTPUT, PFM MODE, FIGURE 4a
CIRCUIT
LOAD AND LINE REGULATION
MAX17503 toc09
OUTPUT VOLTAGE (V)
4.6
4.7
4.8
4.9
5.0
5.1
5.2
5.3
5.4
5.5
4.5
VIN = 36V
VIN = 48V
VIN = 12V
200015001000500
02500
VIN = 24V
LOAD CURRENT (mA)
MODE = OPEN
3.00
3.10
3.20
3.30
3.40
3.50
3.60
0500 1000 1500 2000 2500
OUTPUT VOLTAGE (V)
LOAD CURRENT (mA)
MAX17503S, 3.3V OUTPUT,
PFM MODE,FIGURE 4d CIRCUIT,
LOAD AND L INE REGULATION
V
IN
= 36V
V
IN
= 48V
V
IN
= 12V
V
IN
= 24V
toc10a
4.75
4.8
4.85
4.9
4.95
5
5.05
5.1
5.15
5.2
5.25
0500 1000 1500 2000 2500
OUTPUT VOLTAGE (V)
LOAD CURRENT (mA)
MAX17503S, 5V OUTPUT,
PFM MODE, FIGURE 4c CIRCUIT,
LOAD AND L INE REGULATION
V
IN
= 36V
V
IN
= 48V
V
IN
= 12V
V
IN
= 24V
toc09a
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
7
www.maximintegrated.com
Typical Operating Characteristics (continued)
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS = 5600pF, RT = MODE = open, TA = -40°C to
+125°C, unless otherwise noted. Typical values are at TA = +25ºC. All voltages are referenced to GND, unless otherwise noted.)
MAX17503 SOFT-START/SHUTDOWN FROM EN/UVLO
5V OUTPUT, PFM MODE, 5mA LOAD CURRENT,
FIGURE 4a CIRCUIT
MAX17503 toc14
VRESET
5V/div
VOUT
1V/div
VEN/UVLO
2V/div
2ms/div
MODE = OPEN
MAX17503 SOFT-START/SHUTDOWN FROM EN/UVLO,
3.3V OUTPUT, PFM MODE, 5mA LOAD
CURRENT, FIGURE 4b CIRCUIT
MAX17503 toc15
VRESET
5V/div
VOUT
1V/div
VEN/UVLO
2V/div
2ms/div
MODE = OPEN
MAX17503 SOFT-START/SHUTDOWN FROM EN/UVLO
3.3V OUTPUT, 2.5A LOAD CURRENT,
FIGURE 4b CIRCUIT
MAX17503 toc13
VRESET
5V/div
IOUT
1A/div
VOUT
2V/div
VEN/UVLO
2V/div
1ms/div
1A/div
1mS/div
V
EN/UVLO
5V/div
MAX17503S, SOFT-START/
SHUTDOWN FROM EN/UVL O, 3.3V OUTPUT,
2.5A LOAD CURRENT, FIGURE 4dCIRCUIT)
V
OUT
I
OUT
2V/div
5V/div
toc13a
V
RESET
2mS/div
V
EN/UVLO
5V/div
MAX17503S, SOFT-START/SHUTDOWN
FROM EN/UVL O, 5V OUTPUT, PFM MODE 5MA
LOAD CURRENT, FIGURE 4cCIRCUIT)
V
OUT
1V/div
5V/div
toc14a
V
RESET
2mS/div
V
EN/UVLO
5/div
MAX17503S, SOFT-START/SHUTDOWN
FROM EN/UVLO, 3.3V OUTPUT,PFM MODE 5MA
LOAD CURRENT, FIGURE 4dCIRCUIT)
V
OUT
1V/div
5V/div
toc15a
V
RESET
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
8
www.maximintegrated.com
Typical Operating Characteristics (continued)
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS = 5600pF, RT = MODE = open, TA = -40°C to
+125°C, unless otherwise noted. Typical values are at TA = +25ºC. All voltages are referenced to GND, unless otherwise noted.)
MAX17503 5V OUTPUT, 2.5A LOAD CURRENT
STEADY-STATE SWITCHING WAVEFORMS,
FIGURE 4a CIRCUIT
MAX17503 toc18
ILX
1A/div
VLX
10V/div
VOUT (AC)
50mV/div
1µs/div
400nS/div
V
LX
50mV/div
MAX17503S, STEADY-STATE
SWITCHING WAVEFORMS, 5V OUTPUT,
2.5A LOAD CURRENT, FIGURE 4cCIRCUIT
V
OUT
(AC)
10V/div
2A/div
toc18a
I
LX
MAX17503 5V OUTPUT, PWM MODE
SOFT-START WITH 2.5V PREBIAS,
FIGURE 4a CIRCUIT
MAX17503 toc16
VRESET
5V/div
VOUT
2V/div
VEN/UVLO
2V/div
1ms/div
MODE = SGND
1mS/div
V
EN/UVLO
5V/div
MAX17503S, SOFT-START WITH 2.5V PREBIAS,
5V OUTPUT, PWM MODE, FIGURE 4cCIRCUIT
V
OUT
2V/div
5V/div
toc16a
V
RESET
MAX17503 3.3V OUTPUT, PFM MODE
SOFT-START WITH 2.5V PREBIAS,
FIGURE 4b CIRCUIT
MAX17503 toc17
VRESET
5V/div
VOUT
1V/div
VEN/UVLO
2V/div
1ms/div
MODE = OPEN
1mS/div
V
EN/UVLO
5V/div
MAX17503S, SOFT-START WITH 2.5V PREBIAS,
3.3V OUTPUT, PWM MODE, FIGURE 4dCIRCUIT
V
OUT
1V/div
5V/div
V
RESET
toc17a
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
9
www.maximintegrated.com
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MAX17503 5V OUTPUT, PFM MODE, 25mA LOAD
STEADY-STATE SWITCHING WAVEFORMS,
FIGURE 4a CIRCUIT
MAX17503 toc20
ILX
500mA/div
VLX
10V/div
VOUT (AC)
100mV/div
10µs/div
MODE = OPEN
4μs/div
VLX
100mV/div
MAX17503S, STEADY-STATE
SWITCHING WAVEFORMS, 5V OUTPUT, PFM MODE,
25mA LOAD CURRENT, FIGURE 4c CIRCUIT
VOUT
(AC)
10V/div
500mA/div
toc20a
I
LX
MAX17503 5V OUTPUT, DCM MODE, 25mA LOAD
STEADY-STATE SWITCHING WAVEFORMS,
FIGURE 4a CIRCUIT
MAX17503 toc21
ILX
200mA/div
VLX
10V/div
VOUT (AC)
20mV/div
1µs/div
MODE = VCC
1μs/div
V
LX
20mV/div
MAX17503S, STEADY-STATE
SWITCHING WAVEFORMS, 5V OUTPUT, DCM MODE,
25mA LOAD CURRENT, FIGURE 4c CIRCUIT
V
OUT
(AC)
10V/div
200mA/div
toc21a
I
LX
MAX17503 5V OUTPUT, PWM MODE, NO LOAD
STEADY-STATE SWITCHING WAVEFORMS,
FIGURE 4a CIRCUIT
MAX17503 toc19
ILX
500mA/div
VLX
10V/div
VOUT (AC)
50mV/div
1µs/div
MODE = SGND
400ns/div
V
LX
50mV/div
MAX17503S, STEADY-STATE
SWITCHING WAVEFORMS, 5V OUTPUT,
NO LOAD CURRENT, FIGURE 4c CIRCUIT
V
OUT
(AC)
10V/div
500mA/div
I
LX
toc19a
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
10
www.maximintegrated.com
Typical Operating Characteristics (continued)
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS = 5600pF, RT = MODE = open, TA = -40°C to
+125°C, unless otherwise noted. Typical values are at TA = +25ºC. All voltages are referenced to GND, unless otherwise noted.)
MAX17503 5V OUTPUT, PWM MODE (LOAD CURRENT
STEPPED FROM NO-LOAD TO 1A),
FIGURE 4a CIRCUIT
MAX17503 toc24
I
OUT
1A/div
V
OUT
(AC)
100mV/div
40µs/div
MODE = SGND
40μS/div
100mV/div
MAX17503S, 5V OUTPUT,
PWM MODE, F IGURE 4cCIRCUIT
(LOAD CURRENT STEPPED FROM NO LOAD TO 1A)
V
OUT
AC
1A/div
I
LX
toc24a
MAX17503 5V OUTPUT, PWM MODE
(LOAD CURRENT STEPPED FROM 1A TO 2A),
FIGURE 4a CIRCUIT
MAX17503 toc22
IOUT
1A/div
VOUT (AC)
100mV/div
40µs/div
MODE = SGND
40µS/div
100mV/div
MAX17503S, 5V OUTPUT,
PWM MODE, FIGURE 4c CIRCUIT
(L OAD CURRENT STEPPED FROM 1A TO 2A)
V
OUT
AC
1A/div
toc22a
I
LX
MAX17503 3.3V OUTPUT, PWM MODE
(LOAD CURRENT STEPPED FROM 1A TO 2A),
FIGURE 4b CIRCUIT
MAX17503 toc23
IOUT
1A/div
VOUT (AC)
50mV/div
40µs/div
MODE = SGND
40μS/div
50mV/div
MAX17503S, 3.3V OUTPUT,
PWM MODE, FIGURE 4d CIRCUIT
(L OAD CURRENT STEPPED FROM 1A TO 2A)
V
OUT
AC
2A/div
toc23a
I
LX
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
11
www.maximintegrated.com
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MAX17503 5V OUTPUT, PFM MODE (LOAD CURRENT
STEPPED FROM 5mA TO 1A),
FIGURE 4a CIRCUIT
MAX17503 toc26
IOUT
500mA/div
VOUT
(AC)
100mV/div
2ms/div
MODE = OPEN
MAX17503 3.3V OUTPUT, PFM MODE (LOAD CURRENT
STEPPED FROM 5mA TO 1A),
FIGURE 4b CIRCUIT
MAX17503 toc27
I
OUT
500mA/div
V
OUT
(AC)
50mV/div
2ms/div
MODE = OPEN
MAX17503 3.3V OUTPUT, PWM MODE (LOAD CURRENT
STEPPED FROM NO-LOAD TO 1A),
FIGURE 4b CIRCUIT
MAX17503 toc25
IOUT
1A/div
VOUT
(AC)
50mV/div
40µs/div
MODE = SGND
40μS/div
50mV/div
MAX17503S, 3.3V OUTPUT,
PWM MODE, F IGURE 4dCIRCUIT
(LOAD CURRENT STEPPED FROM NO LOAD TO 1A)
V
OUT
AC
1A/div
toc25a
I
LX
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
12
www.maximintegrated.com
Typical Operating Characteristics (continued)
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS = 5600pF, RT = MODE = open, TA = -40°C to
+125°C, unless otherwise noted. Typical values are at TA = +25ºC. All voltages are referenced to GND, unless otherwise noted.)
MAX17503 5V OUTPUT, OVERLOAD PROTECTION,
FIGURE 4a CIRCUIT
MAX17503 toc30
I
OUT
1A/div
V
OUT
500mV/div
20ms/div
1A/div
10ms/div
V
OUT
200mV/div
MAX17503S, OVERL OAD PROTECTION
5V OUTPUT, FIGURE 4c CIRCUIT
toc30a
I
OUT
MAX17503 5V OUTPUT, DCM MODE (LOAD CURRENT
STEPPED FROM 50mA TO 1A),
FIGURE 4a CIRCUIT
MAX17503 toc28
I
OUT
500mA/div
V
OUT
(AC)
100mV/div
200µs/div
MODE = V
CC
500mA/div
200μs/div
V
OUT
(AC) 100mV/div
MAX17503S, 5V OUTPUT, DCM MODE
(L OAD CURRENT STEPPED FROM 50mA TO 1A)
FIGURE 4c CIRCUIT
toc28a
I
OUT
MAX17503 3.3V OUTPUT, DCM MODE (LOAD CURRENT
STEPPED FROM 50mA TO 1A),
FIGURE 4b CIRCUIT
MAX17503 toc29
IOUT
500mA/div
VOUT (AC)
100mV/div
200µs/div
MODE = VCC
500mA/div
200μs/div
V
OUT
(AC) 100mV/div
MAX17503S, 3.3V OUTPUT, DCM MODE
(L OAD CURRENT STEPPED FROM 50mA TO 1A)
FIGURE 4d CIRCUIT
toc29a
I
OUT
Maxim Integrated
│
13
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MAX17503 5V OUTPUT, 2.5A LOAD CURRENT
BODE PLOT,
FIGURE 4a CIRCUIT
FREQUENCY (Hz)
GAIN (dB)
10k
-30
-20
-10
0
10
20
30
40
50
-40
-60
-40
-20
0
20
40
60
80
100
-80
1k
2 4 6 8 1 2 4 6 8 1 2
100k
MAX17503 toc32
PHASE (°)
CROSSOVER
FREQUENCY = 58.2kHz
PHASE MARGIN = 63.4°
GAIN
PHASE
-50 -100
MAX17503 5V OUTPUT, APPLICATION OF
EXTERNAL CLOCK AT 700kHz,
FIGURE 4a CIRCUIT
MAX17503 toc31
V
SYNC
2V/div
V
LX
10V/div
2µs/div
MODE = SGND
2V/div
2µs/div
V
LX
10V/div
MAX17503S, APPLICATION OF
EXTERNAL CLOCK AT 1.2MHz,
5V OUTPUT, FIGURE 4c CIRCUIT
toc31a
V
SYNC
MAX17503 5V OUTPUT, 2.5A LOAD CURRENT
BODE PLOT,
FIGURE 4b CIRCUIT
FREQUENCY (Hz)
GAIN (dB)
10k
-30
-20
-10
0
10
20
30
40
50
-40
-60
-40
-20
0
20
40
60
80
100
-80
1k
2 4 6 8 1 2 4 6 8 1 2
100k
MAX17503 toc33
PHASE (°)
CROSSOVER
FREQUENCY = 62.5kHz
PHASE MARGIN = 61.2°
GAIN
PHASE
60 120
GAIN (dB)
FRE QUENCY (Hz)
MAX17503S, 3.3V OUTPUT, 2.5A LOAD CURRENT,
BODE PLOT, FIGURE 4c CIRCUIT
CROSSOVER FREQUENCY = 77.5kHz,
PHASE MARGIN = 64.7°
GAIN
PHASE
toc33a
PHASE (°)
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
14
www.maximintegrated.com
Typical Operating Characteristics (continued)
PIN NAME FUNCTION
1–3 VIN
Power-Supply Input. 4.5V to 60V input supply range. Connect the VIN pins together. Decouple to PGND
with a 2.2µF capacitor; place the capacitor close to the VIN and PGND pins. Refer to the MAX17503/
MAX17503S EV kit data sheets for a layout example.
4 EN/UVLO
Enable/Undervoltage Lockout. Drive EN/UVLO high to enable the output voltage. Connect to the center
of the resistor-divider between VIN and SGND to set the input voltage at which the device turns on. Pull
up to VIN for always-on operation.
5RESET Open-Drain RESET Output. The RESET output is driven low if FB drops below 92% of its set value.
RESET goes high 1024 clock cycles after FB rises above 95% of its set value.
6 SYNC The device can be synchronized to an external clock using this pin. See the External Frequency
Synchronization (SYNC) section for more details.
7 SS Soft-Start Input. Connect a capacitor from SS to SGND to set the soft-start time.
8 CF At switching frequencies lower than 500kHz, connect a capacitor from CF to FB. Leave CF open if
switching frequency is equal or more than 500kHz. See the Loop Compensation section for more details.
9 FB Feedback Input. Connect FB to the center tap of an external resistor-divider from the output to GND to
set the output voltage. See the Adjusting Output Voltage section for more details.
10 RT Connect a resistor from RT to SGND to set the regulator’s switching frequency. Leave RT open for the
default 500kHz frequency. See the Setting the Switching Frequency (RT) section for more details.
11 MODE
MODE pin congures the device to operate either in PWM, PFM, or DCM modes of operation. Leave
MODE unconnected for PFM operation (pulse skipping at light loads). Connect MODE to SGND for
constant-frequency PWM operation at all loads. Connect MODE to VCC for DCM operation. See the
Mode Selection (MODE) section for more details.
19
20
* EXPOSED PAD (CONNECT TO GROUND).
18
17
7
6
8
VIN
RESET
9
VIN
PGND
VCC
MODE
PGND
1 2
LX
4 5
15 14 12 11
LX
BST
FB
CF
SS
SYNC
+
VIN SGND
3
13
LX
16 10 RT
PGND
TQFN
4mm × 4mm
MAX17503
TOP VIEW
EN/UVLO
MAX17503/
MAX17503S
Maxim Integrated
│
15
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Pin Description
Pin Conguration
PIN NAME FUNCTION
12 VCC 5V LDO Output. Bypass VCC with 2.2µF ceramic capacitance to SGND.
13 SGND Analog Ground
14–16 PGND
Power Ground. Connect the PGND pins externally to the power ground plane. Connect the SGND and
PGND pins together at the ground return path of the VCC bypass capacitor. Refer to the MAX17503/
MAX17503S EV kit data sheets for a layout example.
17–19 LX Switching Node. Connect LX pins to the switching side of the inductor. Refer to the MAX17503/
MAX17503S EV kit data sheets for a layout example.
20 BST Boost Flying Capacitor. Connect a 0.1µF ceramic capacitor between BST and LX.
— EP
Exposed pad. Connect to the SGND pin. Connect to a large copper plane below the IC to improve heat
dissipation capability. Add thermal vias below the exposed pad. Refer to the MAX17503/MAX17503S EV
kit data sheets for a layout example.
VCC
SGND
1.215V
5V
LX
PGND
MODE
VIN
BST
LDO
EN/UVLO
RT
MAX17503/MAX17503S
SYNC
CF
FB
SS
FB
OSCILLATOR
SWITCHOVER
LOGIC
ERROR AMPLIFIER/
LOOP COMPENSATION
MODE
SELECTION
LOGIC
SLOPE
COMPENSATION
RESET
LOGIC
CURRENT-SENSE
LOGIC
HICCUP
HICCUP
5µA
VCC
PWM/
PFM/
HICCUP
LOGIC
AND
DRIVERS
VBG = 0.9V
RESET
EN/UVLO
Maxim Integrated
│
16
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Pin Description (continued)
Block Diagram
Detailed Description
The MAX17503/MAX17503S high-efficiency, high-
voltage, synchro nously rectified step-down converter with
dual integrated MOSFETs operates over a 4.5V to 60V
input. It delivers up to 2.5A and 0.9V to 90%VIN output
voltage. Built-in compensation across the output voltage
range eliminates the need for external components. The
feedback (FB) regulation accuracy over -40NC to +125NC
is ±1.1%.
The device features a peak-current-mode control
architecture. An internal transconductance error amplifier
produces an integrated error voltage at an internal node,
which sets the duty cycle using a PWM comparator, a high-
side current-sense amplifier, and a slope-compensation
generator. At each rising edge of the clock, the high-
side MOSFET turns on and remains on until either
the appropriate or maximum duty cycle is reached, or
the peak current limit is detected. During the high-side
MOSFET’s on-time, the inductor current ramps up. During
the second half of the switching cycle, the high-side
MOSFET turns off and the low-side MOSFET turns on.
The inductor releases the stored energy as its current
ramps down and provides current to the output.
The device features a MODE pin that can be used to operate
the device in PWM, PFM, or DCM control schemes. The
device integrates adjustable-input undervoltage lockout,
adjustable soft-start, open RESET, and external frequency
synchronization features. The MAX17503S offers a
lower Minimum On-Time that allows for higher switching
frequencies and a smaller solution size.
Mode Selection (MODE)
The logic state of the MODE pin is latched when VCC
and EN/UVLO voltages exceed the respective UVLO
rising thresholds and all internal voltages are ready to
allow LX switching. If the MODE pin is open at power-up,
the device operates in PFM mode at light loads. If the
MODE pin is grounded at power-up, the device operates
in constant-frequency PWM mode at all loads. Finally,
if the MODE pin is connected to VCC at power-up, the
device operates in constant-frequency DCM mode at light
loads. State changes on the MODE pin are ignored during
normal operation.
PWM Mode Operation
In PWM mode, the inductor current is allowed to go
negative. PWM operation provides constant frequency
operation at all loads, and is useful in applications
sensitive to switching frequency. However, the PWM
mode of operation gives lower efficiency at light loads
compared to PFM and DCM modes of operation.
PFM Mode Operation
PFM mode of operation disables negative inductor current
and additionally skips pulses at light loads for high
efficiency. In PFM mode, the inductor current is forced to
a fixed peak of 750mA every clock cycle until the output
rises to 102.3% of the nominal voltage. Once the output
reaches 102.3% of the nominal voltage, both the high-side
and low-side FETs are turned off and the device enters
hibernate operation until the load discharges the output to
101.1% of the nominal voltage. Most of the internal blocks
are turned off in hibernate operation to save quiescent
current. After the output falls below 101.1% of the nominal
voltage, the device comes out of hibernate operation,
turns on all internal blocks, and again commences the
process of delivering pulses of energy to the output until it
reaches 102.3% of the nominal output voltage.
The advantage of the PFM mode is higher efficiency at
light loads because of lower quiescent current drawn from
supply. The disadvantage is that the output-voltage ripple
is higher compared to PWM or DCM modes of operation
and switching frequency is not constant at light loads.
DCM Mode Operation
DCM mode of operation features constant frequency
operation down to lighter loads than PFM mode, by not
skipping pulses but only disabling negative inductor cur-
rent at light loads. DCM operation offers efficiency perfor-
mance that lies between PWM and PFM modes.
Linear Regulator (VCC)
An internal linear regulator (VCC) provides a 5V nominal
supply to power the internal blocks and the low-side
MOSFET driver. The output of the linear regulator (VCC)
should be bypassed with a 2.2µF ceramic capacitor to
SGND. The device employs an undervoltage lockout
circuit that disables the internal linear regulator when VCC
falls below 3.8V (typ).
Maxim Integrated
│
17
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Setting the Switching Frequency (RT)
The switching frequency of the device can be programmed
from 100kHz to 2.2MHz by using a resistor connected
from the RT pin to SGND. The switching frequency (fSW)
is related to the resistor connected at the RT pin (RRT) by
the following equation:
3
RT
SW
21 10
R 1.7
f
×
≅−
where RRT is in kΩ and fSW is in kHz. Leaving the RT pin
open causes the device to operate at the default switching
frequency of 500kHz. See Table 1 for RT resistor values
for a few common switching frequencies. To operate the
MAX17503/MAX17503S at switching frequencies lower
than 200kHz, an R-C network has to be connected in
parallel to the resistor connected from RT to SGND, as
shown in Figure 1. The values of the components R8 and
C13 are 90.9kW and 220pF, respectively.
Operating Input Voltage Range
The minimum and maximum operating input voltages for
a given output voltage should be calculated as follows:
OUT OUT(MAX) DCR
IN(MIN) SW(MAX) OFF(MAX)
OUT(MAX)
V (I (R 0.15))
V1- (f t )
(I 0.175)
+ ×+
=×
+×
OUT
IN(MAX) SW(MAX) ON(MIN)
V
Vft
=×
where VOUT is the steady-state output voltage, IOUT (MAX)
is the maximum load current, RDCR is the DC resistance of
the inductor, fSW(MAX) is the maximum switching frequency,
tOFF-MAX is the worst-case minimum switch off-time (160ns),
and tON-MIN is the worst-case minimum switch on-time
(135ns for the MAX17503, 80ns for the MAX17503S).
External Frequency Synchronization (SYNC)
The internal oscillator of the device can be synchronized
to an external clock signal on the SYNC pin. The external
synchronization clock frequency must be between 1.1
x fSW and 1.4 x fSW, where fSW is the frequency
programmed by the RT resistor. The minimum external
clock pulse-width high should be greater than 50ns. See
the RT AND SYNC section in the Electrical Characteristics
table for details.
Overcurrent Protection/Hiccup Mode
The device is provided with a robust overcurrent protection
scheme that protects the device under overload and
output short-circuit conditions. A cycle-by-cycle peak
current limit turns off the high-side MOSFET whenever
the high-side switch current exceeds an internal limit
of 3.7A (typ). A runaway current limit on the high-side
switch current at 4.3A (typ) protects the device under
high input voltage, short-circuit conditions when there
is insufficient output voltage available to restore the
inductor current that was built up during the on-period of
the step-down converter. One occurrence of the runaway
current limit triggers a hiccup mode. In addition, if due to
a fault condition, feedback voltage drops to 0.58V (typ)
any time after soft-start is complete, and hiccup mode
is triggered. In hiccup mode, the converter is protected
by suspending switching for a hiccup timeout period of
32,768 clock cycles. Once the hiccup timeout period
expires, soft-start is attempted again. Note that when soft-
start is attempted under overload condition, if feedback
voltage does not exceed 0.58V, the device switches at
half the programmed switching frequency. Hiccup mode
of operation ensures low power dissipation under output
short-circuit conditions.
Table 1. Switching Frequency vs. RT
Resistor
Figure 1. Setting the Switching Frequency
SWITCHING FREQUENCY (kHz) RT RESISTOR (kΩ)
500 Open
100 210
200 102
400 49.9
1000 19.1
2200 8.06
Maxim Integrated
│
18
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
R5 R8
C13
RESET Output
The device includes a RESET comparator to monitor the
output voltage. The open-drain RESET output requires an
external pullup resistor. RESET goes high (high impedance)
1024 switching cycles after the regulator output increases
above 95% of the designed nominal regulated voltage.
RESET goes low when the regulator output voltage drops
to below 92% of the nominal regulated voltage. RESET
also goes low during thermal shutdown.
Prebiased Output
When the device starts into a prebiased output, both the
high-side and the low-side switches are turned off so that
the converter does not sink current from the output. High-
side and low-side switches do not start switching until
the PWM comparator commands the first PWM pulse, at
which point switching commences. The output voltage is
then smoothly ramped up to the target value in alignment
with the internal reference.
Thermal-Shutdown Protection
Thermal-shutdown protection limits total power dissipation
in the device. When the junction temperature of the device
exceeds +165°C, an on-chip thermal sensor shuts down
the device, allowing the device to cool. The thermal sensor
turns the device on again after the junction temperature
cools by 10ºC. Soft-start resets during thermal shutdown.
Carefully evaluate the total power dissipation (see the
Power Dissipation section) to avoid unwanted triggering of
the thermal shutdown in normal operation.
Applications Information
Input Capacitor Selection
The input filter capacitor reduces peak currents drawn
from the power source and reduces noise and voltage
ripple on the input caused by the circuit’s switching.
The input capacitor RMS current requirement (IRMS) is
defined by the following equation:
×
= × OUT IN OUT
RMS OUT(MAX)
IN
V (V - V )
II V
where, IOUT(MAX) is the maximum load current. IRMS has
a maximum value when the input voltage equals twice
the output voltage (VIN = 2 x VOUT), so IRMS(MAX) =
IOUT(MAX)/2.
Choose an input capacitor that exhibits less than +10ºC
temperature rise at the RMS input current for optimal
long-term reliability. Use low-ESR ceramic capacitors with
high-ripple-current capability at the input. X7R capacitors
are recommended in industrial applications for their
temperature stability. Calculate the input capacitance
using the following equation:
××
=η× ×∆
OUT(MAX)
IN
SW IN
I D (1- D)
CfV
where D = VOUT/VIN is the duty ratio of the controller,
fSW is the switching frequency, ΔVIN is the allowable input
voltage ripple, and E is the efficiency.
In applications where the source is located distant from
the device input, an electrolytic capacitor should be
added in parallel to the ceramic capacitor to provide
necessary damping for potential oscillations caused by
the inductance of the longer input power path and input
ceramic capacitor.
Inductor Selection
Three key inductor parameters must be specified for
operation with the device: inductance value (L), inductor
saturation current (ISAT), and DC resistance (RDCR). The
switching frequency and output voltage determine the
inductor value as follows:
OUT
SW
V
Lf
=
where VOUT, and fSW are nominal values.
Select a low-loss inductor closest to the calculated
value with acceptable dimensions and having the lowest
possible DC resistance. The saturation current rating
(ISAT) of the inductor must be high enough to ensure that
saturation can occur only above the peak current-limit
value of 3.7A.
Output Capacitor Selection
X7R ceramic output capacitors are preferred due to their
stability over temperature in industrial applications. The
output capacitors are usually sized to support a step load
of 50% of the maximum output current in the application,
so the output voltage deviation is contained to 3% of the
output voltage change. The minimum required output
capacitance can be calculated as follows:
×
= × ∆
STEP RESPONSE
OUT OUT
It
1
C2V
≅+
RESPONSE
C sw
0.33 1
t ()
ff
where ISTEP is the load current step, tRESPONSE is the
response time of the controller, DVOUT is the allowable
output-voltage deviation, fC is the target closed-loop
crossover frequency, and fSW is the switching frequency.
Maxim Integrated
│
19
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
For the MAX17503, select fC to be 1/9th of fSW if the
switching frequency is less than or equal to 500kHz. If the
switching frequency is more than 500kHz, select fC to be
55kHz. For the MAX17503S, select fC to be 1/10th of fSW
if the switching frequency is less than or equal to 1MHz.
If the switching frequency is more than 1MHz, select fC
to be 100kHz.
Derating of ceramic capacitors with DC-voltage must be
considered while selecting the output capacitor. Derating
curves are available from all major ceramic capacitor vendors.
Soft-Start Capacitor Selection
The device implements adjustable soft-start operation to
reduce inrush current. A capacitor connected from the SS pin
to SGND programs the soft-start time. The selected output
capacitance (CSEL) and the output voltage (VOUT) determine
the minimum required soft-start capacitor as follows:
-6
SS SEL OUT
C 28 10 C V
≥× × ×
The soft-start time (tSS) is related to the capacitor
connected at SS (CSS) by the following equation:
SS
SS -6
C
t
5.55 10
=
×
For example, to program a 1ms soft-start time, a 5.6nF
capacitor should be connected from the SS pin to SGND.
Setting the Input Undervoltage-Lockout Level
The device offers an adjustable input undervoltage-lockout
level. Set the voltage at which the device turns on with
a resistive voltage-divider connected from VIN to SGND.
Connect the center node of the divider to EN/UVLO.
Choose R1 to be 3.3MI and then calculate R2 as follows:
×
=
INU
R1 1.215
R2 (V - 1.215)
where VINU is the voltage at which the device is required
to turn on. Ensure that VINU is higher than 0.8 x VOUT. If
the EN/UVLO pin is driven from an external signal source,
a series resistance of minimum 1kΩ is recommended to
be placed between the signal source output and the EN/
UVLO pin, to reduce voltage ringing on the line.
Loop Compensation
The device is internally loop compensated. However, if
the switching frequency is less than 500kHz, connect a
0402 capacitor C6 between the CF pin and the FB pin.
Use Table 2 to select the value of C6.
If the switching frequency is less than 200kHz, connect
an additional R-C network in parallel to the top resistor of
the feedback divider (R3). See Figure 5 to calculate the
values of the components R7, C12, and C6.
Figure 2. Setting the Input Undervoltage Lockout Figure 3. Setting the Output Voltage
Table 2. C6 Capacitor Value at Various
Switching Frequencies
SWITCHING FREQUENCY RANGE (kHz) C6 (pF)
200 to 300 2.2
300 to 400 1.2
400 to 500 0.75
R3
R4
SGND
FB
VOUT
R1
R2
SGND
EN/UVLO
VIN
Maxim Integrated
│
20
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Adjusting Output Voltage
Set the output voltage with a resistive voltage-divider
connected from the positive terminal of the output
capacitor (VOUT) to SGND (see Figure 3). Connect the
center node of the divider to the FB pin. Use the following
procedure to choose the resistive voltage-divider values:
Calculate resistor R3 from the output to the FB pin as
follows:
3
C OUT
216 10
R3 fC
×
=×
where R3 is in kΩ, crossover frequency fC is in kHz, and
the output capacitor COUT is in µF. For the MAX17503,
choose fC to be 1/9th of the switching frequency, fSW, if
the switching frequency is less than or equal to 500kHz.
If the switching frequency is more than 500kHz, select fC
to be 55kHz. For the MAX17503S, select fC to be 1/10th
of fSW if the switching frequency is less than or equal
to 1MHz. If the switching frequency is more than 1MHz,
select fC to be 100kHz.
Calculate resistor R4 from the FB pin to SGND as follows:
×
=
OUT
R3 0.9
R4 (V - 0.9)
Power Dissipation
At a particular operating condition, the power losses that
lead to temperature rise of the part are estimated as
follows:
()
=××
η
2
LOSS OUT DCR
OUT
1
P (P ( - 1)) - I R
= ×
OUT OUT OUT
P VI
where POUT is the total output power, η is the efficiency
of the converter, and RDCR is the DC resistances of the
inductor. (See the Typical Operating Characteristics for more
information on efficiency at typical operating conditions.)
For a multilayer board, the thermal performance metrics
for the package are given below:
JA 33 C Wθ=°
JC 2CWθ=°
The junction temperature of the device can be estimated
at any given maximum ambient temperature (TA_MAX)
from the equation below:
( )
= +θ ×
J_MAX A_MAX JA LOSS
TT P
If the application has a thermal management system that
ensures that the exposed pad of the device is maintained
at a given temperature (TEP_MAX) by using proper heat
sinks, then the junction temperature of the device can be
estimated at any given maximum ambient temperature
from the equation below:
( )
= +θ ×
J_MAX EP_MAX JC LOSS
TT P
Junction temperature greater than +125°C degrades
operating lifetimes.
PCB Layout Guidelines
All connections carrying pulsed currents must be very
short and as wide as possible. The inductance of these
connections must be kept to an absolute minimum due to
the high di/dt of the currents. Since inductance of a current
carrying loop is proportional to the area enclosed by the
loop, if the loop area is made very small, inductance is
reduced. Additionally, small-current loop areas reduce
radiated EMI.
A ceramic input filter capacitor should be placed close
to the VIN pins of the IC. This eliminates as much trace
inductance effects as possible and gives the IC a cleaner
voltage supply. A bypass capacitor for the VCC pin also
should be placed close to the pin to reduce effects of trace
impedance.
When routing the circuitry around the IC, the analog
small-signal ground and the power ground for switching
currents must be kept separate. They should be connected
together at a point where switching activity is at a
minimum, typically the return terminal of the VCC bypass
capacitor. This helps keep the analog ground quiet.
The ground plane should be kept continuous/unbroken
as far as possible. No trace carrying high switching
current should be placed directly over any ground plane
discontinuity.
PCB layout also affects the thermal performance of the
design. A number of thermal vias that connect to a large
ground plane should be provided under the exposed pad
of the part, for efficient heat dissipation.
For a sample layout that ensures first pass success,
refer to the MAX17503 evaluation kit layout available at
www.maximintegrated.com.
Maxim Integrated
│
21
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
R1
R2
C5
R6
C3C6
R4
R5
R3
C2
VOUT
PLANE
VIN PLANE
C4
PGND PLANE
SYNC
SGND PLANE
MODE
SGND
PGND PLANE
MAX17503/
MAX17503S
LX PLANE
LX PLANE
L1
C1
Maxim Integrated
│
22
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Recommended Component Placement for MAX17503/MAX17503S
R1
R2
C5
R6
C3C6
R4
R5
R3
C2
VOUT
PLANE
VIN PLANE
C4
PGND PLANE
SYNC
SGND PLANE
MODE
SGND
PGND PLANE
MAX17503/
MAX17503S
LX PLANE
LX PLANE
L1
C1
Maxim Integrated
│
23
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Recommended Component Placement for MAX17503/MAX17503S (continued)
Figure 4. MAX17503/MAX17503S Typical Application Circuits
RESET
VIN VIN VIN
BSTRT
SYNC
MODE
VCC
SGND
CF SS
FB
PGNDPGNDPGND
LX
LX
LX
EN/UVLO
MAX17503
L1
10µH
C5
0.1µF
C4
22µF R3
178kΩ
R4
39kΩ
VOUT
5V, 2.5A
VIN
(6.5V TO 60V)
C1
2.2µF
C3
5.6nF
C2
2.2µF
fSW = 500kHz
a) 5V Output, 500kHz Switching Frequency
b)
3.3V Output, 500kHz Switching Frequency
RESET
VIN VIN VIN
BSTRT
SYNC
MODE
VCC
SGND
CF SS
FB
PGNDPGNDPGND
LX
LX
LX
VIN (6.5V TO 60V)
EN/UVLO
MAX17503
L1
6.8µH
C5
0.1µF
C4
47µF R3
127kΩ
R4
47.5kΩ
VOUT
3.3V, 2.5A
C1
2.2uF
C3
5600pF
C2
2.2µF
fSW = 500kHz
VIN
Maxim Integrated
│
24
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Figure 4. MAX17503/MAX17503S Typical Application Circuits (continued)
RT
SYNC
MODE
VCC
SGND
BST
LX
FB
RESET
LX
LX
CF SS PGND PGND PGND
VIN
VINVINEN/UVLO
C4
C2
2.2µF
C3
5.6nF
R3
196KΩ
R4
43.2KΩ
10µF
4.7µH
L1
C5
0.1µF
C1
2.2µF
MAX17503S
C
) 5V Output, 1MHz Switching Frequency
V
OUT
5V,2.5A
V
IN
L1 = 4.7µH (XAL4030, 4mm x 4mm)
R5
19.1KΩ
fSW = 1MHz
RT
SYNC
MODE
VCC
SGND
BST
LX
FB
RESET
LX
LX
CF SS PGND PGND PGND
VIN
VINVINEN/UVLO
C4
C2
2.2µF
C3
5.6nF
R3
115KΩ
R4
43.2KΩ
22µF
3.3µH
L1
C5
0.1µF
C1
2.2µF
MAX17503S
d) 3.3V Output, 1MHz Switching Frequency
V
OUT
3.3V,2.5A
V
IN
L1 = 3.3µH (XAL4030, 4mm x 4mm)
R5
19.1KΩ
fSW = 1MHz
Maxim Integrated
│
25
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Figure 5. MAX17503/MAX17503S Typical Application Circuit—3.3V Output, 100kHz Switching Frequency
Note: All devices operate over the -40ºC to +125ºC tempera-
ture range, unless otherwise noted.
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
PART PIN-PACKAGE
MAX17503ATP+ 20 TQFN 4mm x 4 mm
MAX17503SATP+ 20 TQFN-EP* 4mm x 4 mm
Fsw = 100kHz
MAX17503
RESETB
VOUT
3.3V, 2.5A
EN/UVLO VIN VIN BST
RT
VIN
SYNC
MODE
VCC
SGND
CF
SS
FB
PGND PGND PGND
LX
LX
LX
VIN
C12 = 0.8/ (R5 X Fsw)
R7 = R5/100
C6 = 14/Fsw
R8
90.9k
C2 2.2μF
R5
210k
C13
220pF
C3 33000pF
C6 15pF
C4 100μFC9 100μF
C1 2.2μFC8 2.2μF
C5 0.1μF
C12 47pF
L1
33μH
R3 97.6k
R4 36.5k
R7 1k
Maxim Integrated
│
26
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Chip Information
PROCESS: BiCMOS
Ordering Information
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 8/13 Initial release —
1 4/14 Added description and schematic for operation at 100kHz frequency 1-9, 12-13, 15, 18
2 10/16 Added MAX17503S to data sheet, updated junction temperature, and added
TOCs 1–17
3 4/17 Updated data sheet title 1–27
3.1 Corrected typos 15, 17–18, 21
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim
reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits) shown in the Electrical Character-
istics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. © 2017 Maxim Integrated Products, Inc.
│
27
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
MAX17503 4.5V-60V, 2.5A, High-E󰀩ciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Revision History
Mouser Electronics
Authorized Distributor
Click to View Pricing, Inventory, Delivery & Lifecycle Information:
Maxim Integrated:
MAX17503ATP+ MAX17503EVKITB# MAX17503ATP+T MAX17503SATP+ MAX17503SATP+T