LTC3370
1
3370fb
For more information www.linear.com/LTC3370
Typical applicaTion
FeaTures DescripTion
4-Channel 8A Configurable
Buck DC/DCs
The LT C
®
3370 is a highly flexible multioutput power
supply IC. The device includes four synchronous buck
converters, configured to share eight 1A power stages,
each of which is powered from independent 2.25V to
5.5V inputs.
The DC/DCs are assigned to one of eight power configu-
rations via pin programmable C1-C3 pins. The common
buck switching frequency may be programmed with an
external resistor, synchronized to an external oscillator,
or set to a default internal 2MHz clock.
The operating mode for all DC/DCs may be programmed
via the PLL/MODE pin for Burst Mode or forced continuous
mode operation. A PGOODALL output indicates when all
enabled DC/DCs are within a specified percentage of their
final output value.
To reduce input noise, the buck converters are phased
in 90° steps. Precision enable pin thresholds facilitate
reliable power-up sequencing. The LTC3370 is available
in a 32-lead 5mm × 5mm QFN package.
applicaTions
n 8 × 1A Power Stages Configurable as 2, 3, or 4 Output
Channels
n 8 Unique Output Configurations (1A to 4A Per Channel)
n Independent VIN Supplies for Each DC/DC
(2.25V to 5.5V)
n Low Total No Load Supply Current:
n Zero Current In Shutdown (All Channels Off)
n 63µA One Channel Active in Burst Mode
®
Operation
n 18µA Per Additional Channel
n Precision Enable Pin Thresholds for Autonomous
Sequencing
n 1MHz to 3MHz RT Programmable Frequency
(2MHz Default) or PLL Synchronization
n Temp Monitor Indicates Die Temperature
n PGOODALL Pin Indicates All Enabled Bucks Are in
Regulation
n 32-Lead 5mm × 5mm QFN Package
n General Purpose Multichannel Power Supplies:
Automotive, Industrial, Distributed Power Systems L, LT , LT C , LT M , Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Buck Efficiency vs ILOAD
C3 C2 C1 BUCK1 BUCK2 BUCK3 BUCK4
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
2A
3A
3A
4A
3A
4A
4A
4A
2A
1A
1A
1A
2A
–
–
–
2A
2A
1A
1A
–
2A
1A
–
2A
2A
3A
2A
3A
2A
3A
4A
2.25V TO 5.5VVINA
VINB
VINE
VINF
VINC
VIND
VING
VINH
SWA
SWB
SWE
SWF
2.25V TO 5.5V
VOUT1
1.2V/2A
VOUT3
1.8V/2A
VOUT4
2.5V/2A
VOUT2
1.5V/2A
324k
649k
402k
715k
649k
806k
649k
665k
309k
2.7V TO 5.5V
LTC3370
VCC
C1 C2 C3
FB3
EN3
FB1
EN1
2.5V TO 5.5V
SWC
SWD
SWG
SWH
2.25V TO 5.5V
2.2µH 2.2µH
2.2µH
2.2µH
FB4
EN4
FB2
EN2
TEMP
PGOODALL
PLL/MODE
RT
3370 TA01a
GND
LOAD CURRENT (mA)
1
10
100
1000
4000
0
10
20
30
40
50
60
70
80
90
100
EFFICIENCY (%)
3370 TA01b
V
IN
= 3.3V
V
OUT
= 1.8V
f
OSC
= 1MHz
L = 3.3µH
Burst Mode OPERATION
LTC3370
2
3370fb
For more information www.linear.com/LTC3370
Table oF conTenTs
Features ............................................................................................................................ 1
Applications ....................................................................................................................... 1
Typical Application ............................................................................................................... 1
Description......................................................................................................................... 1
Absolute Maximum Ratings ..................................................................................................... 3
Order Information ................................................................................................................. 3
Pin Configuration ................................................................................................................. 3
Electrical Characteristics ........................................................................................................ 4
Typical Performance Characteristics .......................................................................................... 6
Pin Functions .....................................................................................................................12
Block Diagram ....................................................................................................................14
Operation..........................................................................................................................15
Buck Switching Regulators ....................................................................................................................................15
Buck Regulators with Combined Power Stages .....................................................................................................15
Power Failure Reporting Via PGOODALL Pin .........................................................................................................16
Temperature Monitoring and Overtemperature Protection .....................................................................................16
Programming the Operating Frequency .................................................................................................................16
Applications Information .......................................................................................................17
Buck Switching Regulator Output Voltage and Feedback Network ........................................................................17
Buck Regulators ....................................................................................................................................................17
Combined Buck Power Stages ...............................................................................................................................17
Input and Output Decoupling Capacitor Selection..................................................................................................17
PCB Considerations ...............................................................................................................................................19
Typical Applications .............................................................................................................20
Package Description ............................................................................................................23
Typical Application ..............................................................................................................24
Related Parts .....................................................................................................................24
LTC3370
3
3370fb
For more information www.linear.com/LTC3370
pin conFiguraTionabsoluTe MaxiMuM raTings
VINA-H, FB1-4, EN1-4, VCC, PGOODALL,
RT, PLL/MODE, C1-3 ................................... –0.3V to 6V
TEMP .................. –0.3V to Lesser of (VCC + 0.3V) or 6V
IPGOODALL .................................................................5mA
Operating Junction Temperature Range
(Notes 2, 3) ............................................ –40°C to 150°C
Storage Temperature Range .................. –65°C to 150°C
(Note 1)
orDer inForMaTion
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3370EUH#PBF LTC3370EUH#TRPBF 3370 32-Lead (5mm × 5mm) Plastic QFN –40°C to 125°C
LTC3370IUH#PBF LTC3370IUH#TRPBF 3370 32-Lead (5mm × 5mm) Plastic QFN –40°C to 125°C
LTC3370HUH#PBF LTC3370HUH#TRPBF 3370 32-Lead (5mm × 5mm) Plastic QFN –40°C to 150°C
Consult LT C Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
32 31 30 29 28 27 26 25
9 10 11 12
TOP VIEW
33
GND
UH PACKAGE
32-LEAD (5mm × 5mm) PLASTIC QFN
13 14 15 16
17
18
19
20
21
22
23
24
8
7
6
5
4
3
2
1VINA
SWA
SWB
VINB
VINC
SWC
SWD
VIND
VINH
SWH
SWG
VING
VINF
SWF
SWE
VINE
FB1
EN1
TEMP
VCC
PLL/MODE
RT
EN4
FB4
FB2
EN2
C1
C2
C3
PGOODALL
EN3
FB3
TJMAX = 150°C, θJA = 34°C/W, θJC = 3°C/W
EXPOSED PAD (PIN 33) IS GND, MUST BE SOLDERED TO PCB
(http://www.linear.com/product/LTC3370#orderinfo)
LTC3370
4
3370fb
For more information www.linear.com/LTC3370
elecTrical characTerisTics
The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VCC = VINA-H = 3.3V, unless otherwise specified.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VCC VCC Voltage Range l2.7 5.5 V
VCC(UVLO) Undervoltage Threshold on VCC VCC Voltage Falling
VCC Voltage Rising
l
l
2.325
2.425
2.45
2.55
2.575
2.675
V
V
IVCC(ALLOFF) VCC Input Supply Current All Switching Regulators in Shutdown 0 2.5 µA
IVCC VCC Input Supply Current One Buck Active
PLL/MODE = 0V, RT = 400k, VFB(BUCK) = 0.85V
PLL/MODE = 2MHz
45
170
70
250
µA
µA
fOSC Internal Oscillator Frequency VRT = VCC, PLL/MODE = 0V
VRT = VCC, PLL/MODE = 0V
RT = 400k, PLL/MODE = 0V
l
l
1.8
1.75
1.8
2
2
2
2.2
2.25
2.2
MHz
MHz
MHz
fPLL/MODE Synchronization Frequency tLOW, tHIGH > 40ns l1 3 MHz
VPLL/MODE PLL/MODE Level High
PLL/MODE Level Low
For Synchronization
For Synchronization
l
l
1.2
0.4
V
V
VRT RT Servo Voltage RT = 400k l780 800 820 mV
Temp Monitor
VTEMP(ROOM) TEMP Voltage at 25°C 180 220 260 mV
ΔVTEMP/°C VTEMP Slope 7 mV/°C
OT Overtemperature Shutdown 170 °C
OT Hyst Overtemperature Hysteresis 10 °C
1A Buck Regulators
VIN Buck Input Voltage Range l2.25 5.5 V
VOUT Buck Output Voltage Range lVFB VIN V
VIN(UVLO) Undervoltage Threshold on VIN VIN Voltage Falling
VIN Voltage Rising
l
l
1.95
2.05
2.05
2.15
2.15
2.25
V
V
IVIN Burst Mode Operation Input Current
Forced Continuous Mode Operation
Input Current
Shutdown Input Current
VFB = 0.85V (Note 4)
ISW(BUCK) = 0µA, FB = 0V
18
400
0
30
600
2.5
µA
µA
µA
IFWD PMOS Current Limit (Note 5) 1.9 2.3 2.7 A
VFB1 Feedback Regulation Voltage for Buck 1 l792 800 808 mV
VFB Feedback Regulation Voltage for
Bucks 2-4
l780 800 820 mV
IFB Feedback Leakage Current VFB = 0.85V –50 50 nA
DMAX Maximum Duty Cycle VFB = 0V l100 %
RPMOS PMOS On-Resistance ISW = 100mA 300 mΩ
RNMOS NMOS On-Resistance ISW = –100mA 240 mΩ
ILEAKP PMOS Leakage Current EN = 0 –2 2 µA
ILEAKN NMOS Leakage Current EN = 0 –2 2 µA
tSS Soft-Start Time 1 ms
VPGOOD(FALL) Falling PGOOD Threshold for Buck 1 % of Regulated VFB 96.8 98 99.2 %
Falling PGOOD Threshold for Bucks 2 to 4 % of Regulated VFB 93 95 97 %
VPGOOD(HYS) PGOOD Hysteresis for Bucks 1 to 4 % of Regulated VFB 0.3 %
LTC3370
5
3370fb
For more information www.linear.com/LTC3370
elecTrical characTerisTics
The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VCC = VINA-H = 3.3V, unless otherwise specified.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Buck Regulators Combined
IFWD2PMOS Current Limit 2 Buck Power Stages Combined (Note 5) 4.6 A
IFWD3PMOS Current Limit 3 Buck Power Stages Combined (Note 5) 6.9 A
IFWD4PMOS Current Limit 4 Buck Power Stages Combined (Note 5) 9.2 A
Interface Logic Pins (PGOODALL, PLL/MODE, CT, C1, C2, C3)
IOH Output High Leakage Current PGOODALL 5.5V at Pin 1 µA
VOL Output Low Voltage PGOODALL 3mA into Pin 0.1 0.4 V
VIL C1, C2, C3 Input Low Threshold l0.4 V
VIH PLL/MODE, CT, C1, C2, C3 Input High
Threshold
lVCC – 0.4 V
VIL PLL/MODE Input Low Threshold lVCC – 1.2 V
Interface Logic Pins (EN1, EN2, EN3, EN4)
VHI(ALLOFF) Enable Rising Threshold All Regulators Disabled l730 1200 mV
VHI Enable Rising Threshold At Least One Regulator Enabled l400 420 mV
VLO Enable Falling Threshold 340 375 mV
IEN Enable Pin Leakage Current EN = 3.3V 1 µA
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC3370 is tested under pulsed load conditions such that
TJ ≈ TA. The LTC3370E is guaranteed to meet specifications from
0°C to 85°C junction temperature. Specifications over the –40°C to
125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTC3370I is guaranteed over the –40°C to 125°C operating junction
temperature range. The LTC3370H is guaranteed over the –40°C to 150°C
operating junction temperature range. High junction temperatures degrade
operating lifetimes; operating lifetime is derated for junction temperatures
greater than 125°C. Note that the maximum ambient temperature
consistent with these specifications is determined by specific operating
conditions in conjunction with board layout, the rated package thermal
impedance and other environmental factors. The junction temperature
(TJ in °C) is calculated from the ambient temperature (TA in °C) and power
dissipation (PD in Watts) according to the formula:
TJ = TA + (PD • θJA)
where θJA (in °C/W) is the package thermal impedance.
Note 3: The LTC3370 includes overtemperature protection which protects
the device during momentary overload conditions. Junction temperatures
will exceed 150°C when overtemperature protection is active. Continuous
operation above the specified maximum operating junction temperature
may impair device reliability.
Note 4: Static current, switches not switching. Actual current may be
higher due to gate charge losses at the switching frequency.
Note 5: The current limit features of this part are intended to protect the
IC from short term or intermittent fault conditions. Continuous operation
above the maximum specified pin current rating may result in device
degradation over time.
LTC3370
6
3370fb
For more information www.linear.com/LTC3370
Typical perForMance characTerisTics
Buck VIN Undervoltage Threshold
vs Temperature
VCC Supply Current vs
Temperature
VCC Supply Current vs
Temperature
RT Programmed Oscillator
Frequency vs Temperature
Default Oscillator Frequency vs
Temperature
Buck Efficiency vs ILOAD Buck Power Loss vs ILOAD
VCC Undervoltage Threshold vs
Temperature
Oscillator Frequency vs VCC
TA = 25°C, unless otherwise noted.
LOAD CURRENT (mA)
EFFICIENCY (%)
3370 G01
100
90
80
40
30
20
10
70
50
60
01 100010010
Burst Mode OPERATION
VIN = 3.3V
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
1A BUCK
2A BUCK
3A BUCK
4A BUCK
POWER LOSS (mW)
3000
2500
1000
500
2000
1500
01 100010010
Burst Mode OPERATION
VIN = 3.3V
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
3370 G02
1A BUCK
2A BUCK
3A BUCK
4A BUCK
LOAD CURRENT (mA)
TEMPERATURE (°C)
–55
–25
5
35
65
95
125
155
2.30
2.35
2.40
2.45
2.50
2.55
2.60
2.65
2.70
UV THRESHOLD (V)
3370 G03
V
CC
RISING
V
CC
FALLING
TEMPERATURE (°C)
–55
–25
5
35
65
95
125
155
1.90
1.95
2.00
2.05
2.10
2.15
2.20
2.25
2.30
UV THRESHOLD (V)
3370 G04
V
IN
RISING
V
IN
FALLING
TEMPERATURE (°C)
–55
–25
5
35
65
95
125
155
1.80
1.85
1.90
1.95
2.00
2.05
2.10
2.15
2.20
f
OSC
(MHz)
3371 G07
V
CC
= 2.7V
V
CC
= 3.3V
V
CC
= 5.5V
R
T
= 400k
TEMPERATURE (°C)
–55
–25
5
35
65
95
125
155
1.80
1.85
1.90
1.95
2.00
2.05
2.10
2.15
2.20
f
OSC
(MHz)
3370 G08
V
CC
= 2.7V
V
CC
= 3.3V
V
CC
= 5.5V
V
RT
= V
CC
VCC (V)
2.7
fOSC (MHz)
2.20
2.15
2.00
1.90
2.10
2.05
1.95
1.85
1.80 3.9 5.13.5 4.7
3370 G09
5.53.1 4.3
VRT = VCC
RT = 400k
AT LEAST ONE BUCK ENABLED
PLL/MODE = 0V
FB = 850mV
V
CC
= 2.7V
V
CC
= 3.3V
V
CC
= 5.5V
TEMPERATURE (°C)
–55
–25
5
35
65
95
125
155
0
25
50
75
100
125
I
VCC
(µA)
3370 G05
AT LEAST ONE BUCK ENABLED
PLL/MODE = 2MHz
TEMPERATURE (°C)
–55
–25
5
35
65
95
125
155
0
40
80
120
160
200
240
280
320
360
400
I
VCC
(µA)
3370 G06
V
CC
= 2.7V
V
CC
= 3.3V
V
CC
= 5.5V
LTC3370
7
3370fb
For more information www.linear.com/LTC3370
Typical perForMance characTerisTics
Enable Pin Precision Threshold
vs Temperature
Enable Threshold vs Temperature
Buck VIN Supply Current vs
Temperature
Buck VIN Supply Current vs
Temperature
VOUT vs Temperature
PMOS Current Limit vs
Temperature
Oscillator Frequency vs RTVTEMP vs Temperature
TA = 25°C, unless otherwise noted.
RT (kΩ)
250
fOSC (MHz)
4.0
3.5
2.0
1.0
3.0
2.5
1.5
0.5
0450400
3370 G10
350300 500 550 600 650 700 750 800
VCC = 3.3V
TEMPERATURE (°C)
–55
–25
5
35
65
95
125
155
–200
0
200
400
600
800
1000
1200
1400
V
TEMP
(mV)
3370 G11
I
LOAD
= 0mA
ACTUAL V
TEMP
IDEAL V
TEMP
V
CC
= 3.3V
TEMPERATURE (°C)
–55
–25
5
35
65
95
125
155
0
10
20
30
40
50
I
VIN_BURST
(µA)
3370 G14
V
IN
= 2.25V
V
IN
= 3.3V
V
IN
= 5.5V
Burst Mode OPERATION
FB = 850mV
TEMPERATURE (°C)
–55
–25
5
35
65
95
125
155
0
50
100
150
200
250
300
350
400
450
500
550
I
VIN_FORCED_CONTINUOUS
(µA)
3370 G15
V
IN
= 2.25V
V
IN
= 3.3V
V
IN
= 5.5V
FORCED CONTINUOUS MODE
FB = 0V
TEMPERATURE (°C)
–55
–25
5
35
65
95
125
155
1.72
1.74
1.76
1.78
1.80
1.82
1.84
1.86
1.88
V
OUT
(V)
3370 G16
V
IN
= 2.25V
V
IN
= 3.3V
V
IN
= 5.5V
I
LOAD
= 0mA
FORCED CONTINUOUS MODE
TEMPERATURE (°C)
–55
–25
5
35
65
95
125
155
2.0
2.1
2.2
2.3
2.4
2.5
2.6
I
FWD
(A)
3370 G17
V
IN
= 3.3V
PMOS RDS(ON) vs Temperature
TEMPERATURE (°C)
–55
–25
5
35
65
95
125
155
150
200
250
300
350
400
450
500
550
R
DS(ON)
(mΩ)
3370 G18
V
IN
= 2.25V
V
IN
= 3.3V
V
IN
= 5.5V
EN RISING
EN FALLING
ALL REGULATORS DISABLED
V
CC
= 3.3V
TEMPERATURE (°C)
–55
–25
5
35
65
95
125
155
350
400
450
500
550
600
650
700
750
800
850
900
EN THRESHOLD (mV)
3370 G12
EN RISING
EN FALLING
TEMPERATURE (°C)
–55
–25
5
35
65
95
125
155
365
370
375
380
385
390
395
400
405
EN THRESHOLD (mV)
3370 G13
LTC3370
8
3370fb
For more information www.linear.com/LTC3370
1A Buck Power Loss vs ILOAD,
VOUT = 1.2V
1A Buck Efficiency vs ILOAD,
VOUT = 1.8V
1A Buck Power Loss vs ILOAD,
VOUT = 1.8V
1A Buck Efficiency vs ILOAD,
VOUT = 2.5V
1A Buck Power Loss vs ILOAD,
VOUT = 2.5V
1A Buck Efficiency vs ILOAD,
VOUT = 3.3V
NMOS RDS(ON) vs Temperature
1A Buck Efficiency vs ILOAD,
VOUT = 1.2V
1A Buck Power Loss vs ILOAD,
VOUT = 3.3V
Typical perForMance characTerisTics
TA = 25°C, unless otherwise noted.
LOAD CURRENT (mA)
EFFICIENCY (%)
3370 G20
100
90
80
40
30
20
10
70
50
60
01 100010010
VOUT = 1.2V
fOSC = 2MHz
L = 2.2µH
FORCED
CONTINUOUS
MODE
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
Burst Mode OPERATION
LOAD CURRENT (mA)
EFFICIENCY (%)
3370 G22
100
90
80
40
30
20
10
70
50
60
01 100010010
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
Burst Mode OPERATION
FORCED
CONTINUOUS
MODE
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
LOAD CURRENT (mA)
POWER LOSS (mW)
3370 G23
1000
900
800
400
300
200
100
700
500
600
01 100010010
VIN = 2.25V
Burst Mode OPERATION
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
VIN = 3.3V
VIN = 5.5V
LOAD CURRENT (mA)
EFFICIENCY (%)
3370 G24
100
90
80
40
30
20
10
70
50
60
01 100010010
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
LOAD CURRENT (mA)
POWER LOSS (mW)
3370 G25
1000
900
800
400
300
200
100
700
500
600
01 100010010
VIN = 2.7V
Burst Mode OPERATION
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
VIN = 3.3V
VIN = 5.5V
LOAD CURRENT (mA)
EFFICIENCY (%)
3370 G26
100
90
80
40
30
20
10
70
50
60
01 100010010
VOUT = 3.3V
fOSC = 2MHz
L = 2.2µH
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
VIN = 4.2V
VIN = 5.5V
VIN = 4.2V
VIN = 5.5V
LOAD CURRENT (mA)
POWER LOSS (mW)
3370 G21
1000
900
800
400
300
200
100
700
500
600
01 100010010
VIN = 2.25V
Burst Mode OPERATION
VOUT = 1.2V
fOSC = 2MHz
L = 2.2µH
VIN = 3.3V
VIN = 5.5V
LOAD CURRENT (mA)
POWER LOSS (mW)
3370 G27
1000
900
800
400
300
200
100
700
500
600
01 100010010
Burst Mode OPERATION
VOUT = 3.3V
fOSC = 2MHz
L = 2.2µH
VIN = 5.5V
VIN = 4.2V
TEMPERATURE (°C)
–55
–25
5
35
65
95
125
155
150
200
250
300
350
400
450
R
DS(ON)
(mΩ)
3370 G19
V
IN
= 2.25V
V
IN
= 3.3V
V
IN
= 5.5V
LTC3370
9
3370fb
For more information www.linear.com/LTC3370
3A Buck Efficiency vs ILOAD,
VOUT = 1.8V
3A Buck Efficiency vs ILOAD,
VOUT = 2.5V
4A Buck Efficiency vs ILOAD,
VOUT = 1.8V
4A Buck Efficiency vs ILOAD,
VOUT = 2.5V
1A Buck Efficiency vs ILOAD
(Across Operating Frequency) 1A Buck Efficiency vs Frequency
(Forced Continuous Mode)
2A Buck Efficiency vs ILOAD,
VOUT = 1.8V
2A Buck Efficiency vs ILOAD,
VOUT = 2.5V
Typical perForMance characTerisTics
TA = 25°C, unless otherwise noted.
LOAD CURRENT (mA)
EFFICIENCY (%)
3370 G28
100
90
80
40
30
20
10
70
50
60
01 100010010
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
LOAD CURRENT (mA)
EFFICIENCY (%)
3370 G29
100
90
80
40
30
20
10
70
50
60
01 100010010
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
LOAD CURRENT (mA)
EFFICIENCY (%)
3370 G30
100
90
80
40
30
20
10
70
50
60
01 100010010
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
LOAD CURRENT (mA)
EFFICIENCY (%)
3370 G31
100
90
80
40
30
20
10
70
50
60
01 100010010
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
LOAD CURRENT (mA)
EFFICIENCY (%)
3370 G32
100
90
80
40
30
20
10
70
50
60
01 100010010
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
LOAD CURRENT (mA)
EFFICIENCY (%)
3370 G33
100
90
80
40
30
20
10
70
50
60
01 100010010
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
LOAD CURRENT (mA)
EFFICIENCY (%)
3370 G34
100
90
80
40
30
20
10
70
50
60
01 100010010
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
fOSC = 1MHz, L = 3.3µH
fOSC = 2MHz, L = 2.2µH
fOSC = 3MHz, L = 1µH
fOSC = 1MHz, L = 3.3µH
fOSC = 2MHz, L = 2.2µH
fOSC = 3MHz, L = 1µH
VOUT = 1.8V
VIN = 3.3V
FREQUENCY (MHz)
EFFICIENCY (%)
3370 G35
100
90
80
40
30
20
10
70
50
60
01 31.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8
VOUT = 1.8V
ILOAD = 100mA
L = 3.3µH
VIN = 3.3V
VIN = 2.25V
VIN = 5.5V
1A Buck Efficiency vs Frequency
(Forced Continuous Mode)
FREQUENCY (MHz)
EFFICIENCY (%)
3370 G36
100
90
80
40
30
20
10
70
50
60
01 31.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8
VOUT = 1.8V
ILOAD = 200mA
L = 3.3µH
VIN = 2.25V
VIN = 5.5V
VIN = 3.3V
LTC3370
10
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For more information www.linear.com/LTC3370
4A Buck Regulator Load Regulation
(Forced Continuous Mode)
1A Buck Regulator Line Regulation
(Forced Continuous Mode)
1A Buck Regulator No-Load Start-Up
Transient(Burst Mode Operation)
1A Buck Regulator No-Load Start-Up
Transient (Forced Continuous Mode)
4A Buck Regulator No-Load Start-Up
Transient (Burst Mode Operation)
4A Buck Regulator No-Load Start-Up
Transient (Forced Continuous Mode)
1A Buck Efficiency vs Frequency
(Forced Continuous Mode)
1A Buck Regulator Load Regulation
(Forced Continuous Mode)
1A Buck Regulator Transient
Response (Burst Mode Operation)
Typical perForMance characTerisTics
TA = 25°C, unless otherwise noted.
FREQUENCY (MHz)
EFFICIENCY (%)
3370 G37
100
90
80
40
30
20
10
70
50
60
01 31.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8
VOUT = 1.8V
VIN = 3.3V
L = 3.3µH
ILOAD = 100mA
ILOAD = 500mA
ILOAD = 20mA
LOAD CURRENT (mA)
VOUT (V)
3370 G38
1.820
1.816
1.812
1.796
1.792
1.788
1.784
1.808
1.800
1.804
1.780 1 100010010
VIN = 5.5V
VIN = 3.3V
VIN = 2.25V
DROPOUT
fOSC = 2MHz
L = 2.2µH
LOAD CURRENT (mA)
VOUT (V)
3370 G39
1.820
1.816
1.812
1.796
1.792
1.788
1.784
1.808
1.800
1.804
1.780 1 100010010
VIN = 3.3V
VIN = 2.25V
fOSC = 2MHz
L = 2.2µH
DROPOUT
VIN = 5.5V
VIN (V)
VOUT (V)
3370 G40
1.820
1.815
1.795
1.790
1.785
1.810
1.800
1.805
1.780
2.25 2.75 3.25 3.75 4.25 4.75 5.25
fOSC = 2MHz
L = 2.2µH
ILOAD = 100mA
ILOAD = 500mA
200µs/DIV
VOUT
500mV/DIV
INDUCTOR
CURRENT
500mA/DIV
EN
2V/DIV
3370 G41
VIN = 3.3V
VOUT = 1.8V
200µs/DIV
VOUT
500mV/DIV
INDUCTOR
CURRENT
500mA/DIV
EN
2V/DIV
3370 G42
VIN = 3.3V
VOUT = 1.8V
200µs/DIV
VOUT
500mV/DIV
INDUCTOR
CURRENT
500mA/DIV
EN
2V/DIV
3370 G43
VIN = 3.3V
VOUT = 1.8V
200µs/DIV
VOUT
500mV/DIV
INDUCTOR
CURRENT
500mA/DIV
EN
2V/DIV
3370 G44
VIN = 3.3V
VOUT = 1.8V
50µs/DIV
VOUT
100mV/DIV
AC-COUPLED
INDUCTOR
CURRENT
200mA/DIV
0mA
3370 G45
LOAD STEP = 100mA TO 700mA
VIN = 3.3V
VOUT = 1.8V
LTC3370
11
3370fb
For more information www.linear.com/LTC3370
4A Buck Regulator Transient
Response (Burst Mode Operation)
4A Buck Regulator Transient
Response (Forced Continuous
Mode)
1A Buck Regulator Transient
Response (Forced Continuous
Mode)
Typical perForMance characTerisTics
TA = 25°C, unless otherwise noted.
50µs/DIV
VOUT
100mV/DIV
AC-COUPLED
INDUCTOR
CURRENT
200mA/DIV
0mA
3370 G46
LOAD STEP = 100mA TO 700mA
VIN = 3.3V
VOUT = 1.8V
50µs/DIV
VOUT
100mV/DIV
AC-COUPLED
INDUCTOR
CURRENT
1A/DIV
0mA
3370 G47
LOAD STEP = 400mA TO 2.8A
VIN = 3.3V
VOUT = 1.8V
50µs/DIV
VOUT
100mV/DIV
AC-COUPLED
INDUCTOR
CURRENT
1A/DIV
0mA
3370 G48
LOAD STEP = 400mA TO 2.8A
VIN = 3.3V
VOUT = 1.8V
pin FuncTions
VINA (Pin 1): Power Stage A Input Supply. Bypass to GND
with a 10µF or larger ceramic capacitor.
SWA (Pin 2): Power Stage A Switch Node. External induc-
tor connects to this pin.
SWB (Pin 3): Power Stage B Switch Node. External induc-
tor connects to this pin.
VINB (Pin 4): Power Stage B Input Supply. Bypass to GND
with a 10µF or larger ceramic capacitor.
VINC (Pin 5): Power Stage C Input Supply. Bypass to GND
with a 10µF or larger ceramic capacitor.
SWC (Pin 6): Power Stage C Switch Node. External induc-
tor connects to this pin.
SWD (Pin 7): Power Stage D Switch Node. External induc-
tor connects to this pin.
VIND (Pin 8): Power Stage D Input Supply. Bypass to GND
with a 10µF or larger ceramic capacitor.
FB2 (Pin 9): Buck Regulator 2 Feedback Pin. Receives
feedback by a resistor divider connected across the output.
In configurations where Buck 2 is not used, FB2 should
be tied to ground.
EN2 (Pin 10): Buck Regulator 2 Enable Input. Active high.
In configurations where Buck 2 is not used, tie EN2 to
ground. Do not float.
C1 (Pin 11): Configuration Control Input Bit. With C2 and
C3, C1 configures the Buck output current power stage
combinations. C1 should either be tied to VCC or ground.
Do not float.
C2 (Pin 12): Configuration Control Input Bit. With C1 and
C3, C2 configures the Buck output current power stage
combinations. C2 should either be tied to VCC or ground.
Do not float.
C3 (Pin 13): Configuration Control Input Bit. With C1 and
C2, C3 configures the Buck output current power stage
combinations. C3 should either be tied to VCC or ground.
Do not float.
PGOODALL (Pin 14): PGOOD Status Pin (Active Low).
Open-drain output. When the regulated output voltage
of any enabled switching regulator is below its PGOOD
threshold level, this pin is driven LOW. This level is 98%
of the programmed output value for Buck 1 and 95% of
LTC3370
12
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For more information www.linear.com/LTC3370
pin FuncTions
the programmed output value for Bucks 2-4. When all
buck regulators are disabled PGOODALL is driven LOW.
EN3 (Pin 15): Buck Regulator 3 Enable Input. Active high.
In configurations where Buck 3 is not used, tie EN3 to
ground. Do not float.
FB3 (Pin 16): Buck Regulator 3 Feedback Pin. Receives
feedback by a resistor divider connected across the output.
In configurations where Buck 3 is not used, FB3 should
be tied to ground.
VINE (Pin 17): Power Stage E Input Supply. Bypass to GND
with a 10µF or larger ceramic capacitor.
SWE (Pin 18): Power Stage E Switch Node. External
inductor connects to this pin.
SWF (Pin 19): Power Stage F Switch Node. External
inductor connects to this pin.
VINF (Pin 20): Power Stage F Input Supply. Bypass to GND
with a 10µF or larger ceramic capacitor.
VING (Pin 21): Power Stage G Input Supply. Bypass to
GND with a 10µF or larger ceramic capacitor.
SWG (Pin 22): Power Stage G Switch Node. External
inductor connects to this pin.
SWH (Pin 23): Power Stage H Switch Node. External
inductor connects to this pin.
VINH (Pin 24): Power Stage H Input Supply. Bypass to
GND with a 10µF or larger ceramic capacitor.
FB4 (PIN 25): Buck Regulator 4 Feedback Pin. Receives
feedback by a resistor divider connected across the output.
EN4 (Pin 26): Buck Regulator 4 Enable Input. Active high.
Do not float.
RT (Pin 27): Oscillator Frequency Pin. This pin provides
two modes of setting the switching frequency. Connecting
a resistor from RT to ground sets the switching frequency
based on the resistor value. If RT is tied to VCC the internal
2MHz oscillator is used. Do not float.
PLL/MODE (Pin 28): Oscillator Synchronization and Buck
Mode Select Pin. Driving PLL/MODE with an external clock
signal synchronizes all switches to the applied frequency,
and the buck converters operate in forced continuous
mode. The slope compensation is automatically adapted
to the external clock frequency. The absence of an external
clock signal enables the frequency programmed by the
RT pin. When not synchronizing to an external clock this
input determines how the LTC3370 operates at light loads.
Pulling this pin to ground selects Burst Mode operation.
Tying this pin to VCC invokes forced continuous mode
operation. Do not float.
VCC (Pin 29): Internal Bias Supply. Bypass to GND with a
10µF or larger ceramic capacitor.
TEMP (Pin 30): Temperature Indication Pin. TEMP outputs
a voltage of 220mV (typical) at 25°C. The TEMP voltage
increases by 7mV/°C (typical) at higher temperatures
giving an external indication of the LTC3370 internal die
temperature.
EN1 (Pin 31): Buck Regulator 1 Enable Input. Active high.
Do not float.
FB1 (Pin 32): Buck Regulator 1 Feedback Pin. Receives
feedback by a resistor divider connected across the output.
GND (Exposed Pad Pin 33): Ground. The exposed pad
should be connected to a continuous ground plane on the
printed circuit board directly under the LTC3370.
LTC3370
13
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For more information www.linear.com/LTC3370
block DiagraM
PGOOD LOGIC
BUCK REGULATOR 1
CONTROL
BANDGAP UVLO
SD
4 PGOOD
VINB
MODE
31 EN1
32 FB1
OSCILLATOR
27 RT
29 VCC
28 PLL/MODE
14 PGOODALL
CLK
REF
OT UV
MODE
BUCK REGULATOR 2
CONTROL
VIND
10
FB2
9
EN2
BUCK REGULATOR 3
CONTROL
VINE
15
FB3
16
EN3
BUCK REGULATOR 4
CONTROL
1A POWER
STAGE H
VING
C2
CONFIGURATION LINES
26 EN4
25 FB4
SD REF CLK
4
12
C1
11
C3
GND
(EXPOSED PAD)
SWH
3370 BD
VINH
13 33
23
24
1A POWER
STAGE G SWG
VING
22
21
1A POWER
STAGE F SWF
VINF
19
20
1A POWER
STAGE E SWE
VINE
18
17
1A POWER
STAGE D SWD
VIND
7
8
1A POWER
STAGE C SWC
VINC
6
5
1A POWER
STAGE B SWB
VINB
3
4
1A POWER
STAGE A
TEMP
MONITOR
SWA
VINA
2
1
TEMP 30
4
C3 C2 C1 BUCK1 BUCK2 BUCK3 BUCK4
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
2A
3A
3A
4A
3A
4A
4A
4A
2A
1A
1A
1A
2A
–
–
–
2A
2A
1A
1A
–
2A
1A
–
2A
2A
3A
2A
3A
2A
3A
4A
LTC3370
14
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For more information www.linear.com/LTC3370
operaTion
Buck Switching Regulators
The LTC3370 contains eight monolithic 1A synchronous
buck switching channels. These are controlled by up to
four current mode regulator controllers. All of the switch-
ing regulators are internally compensated and need only
external feedback resistors to set the output voltage. The
switching regulators offer two operating modes: Burst
Mode operation (PLL/MODE = LOW) for higher efficiency
at light loads and forced continuous PWM mode (PLL/
MODE = HIGH or switching) for lower noise at light loads.
In Burst Mode operation at light loads, the output capacitor
is charged to a voltage slightly higher than its regulation
point. The regulator then goes into a sleep state, during
which time the output capacitor provides the load current.
In sleep most of the regulator’s circuitry is powered down,
helping conserve input power. When the output capaci-
tor droops below its programmed value, the circuitry is
powered on and another burst cycle begins. The sleep
time decreases as load current increases. In Burst Mode
operation, the regulator bursts at light loads whereas at
higher loads it operates at constant frequency PWM mode
operation. In forced continuous mode, the oscillator runs
continuously and the buck switch currents are allowed
to reverse under very light load conditions to maintain
regulation. This mode allows the buck to run at a fixed
frequency with minimal output ripple.
Each buck switching regulator can operate at an indepen-
dent VIN voltage and has its own FB and EN pin to maxi-
mize flexibility. The enable pins have two different enable
threshold voltages that depend on the operating state of
the LTC3370. With all regulators disabled, the enable pin
threshold is set to 730mV (typical). Once any regulator
is enabled, the enable pin thresholds of the remaining
regulators are set to a bandgap-based 400mV and the EN
pins are each monitored by a precision comparator. This
precision EN threshold may be used to provide event-
based sequencing via feedback from other previously
enabled regulators. All buck regulators have forward and
reverse-current limiting, soft-start to limit inrush current
during start-up, and short-circuit protection.
The buck switching regulators are phased in 90° steps to
reduce noise and input ripple. The phase step determines
the fixed edge of the switching sequence, which is when
the PMOS turns on. The PMOS off (NMOS on) phase is
subject to the duty cycle demanded by the regulator. Buck1
is set to 0°, Buck 2 is set to 90°, Buck 3 is set to 270°, and
Buck 4 is set to 180°. In shutdown all SW nodes are high
impedance. The buck regulator enable pins may be tied
to VOUT voltages through a resistor divider, to program
power-up sequencing.
The buck switching regulators feature a controlled shut-
down scheme where the inductor current ramps down to
zero through the NMOS switch. If any event causes the
buck regulator to shut down (EN = LOW, OT, VINA-H or VCC
UVLO) the NMOS switch turns on until the inductor current
reaches 0mA (typical). Then, the switch pin becomes Hi-Z.
Buck Regulators with Combined Power Stages
Up to four adjacent buck regulators may be combined in
a master-slave configuration by setting the configuration
via the C1, C2, and C3 pins. These pins should either be
tied to ground or pin strapped to VCC in accordance with
the desired configuration code (Table 1). Any combined
SW pins must be tied together, as must any of the com-
bined VIN pins. EN1 and FB1 are utilized by Buck 1, EN2
and FB2 by Buck 2, EN3 and FB3 by Buck 3, and EN4 and
FB4 by Buck 4. If any buck is not used or is not available
in the desired configuration, then the associated FB and
EN pins must be tied to ground.
Any available combination of 2, 3, or 4 adjacent Buck
regulators serve to provide up to either 2A, 3A, or 4A
of average output load current. For example, code 110
(C3C2C1) configures Buck 1 to operate as a 4A regula-
tor through VIN/SW pairs A, B, C, and D, while Buck 2
is disabled, Buck 3 operates as a 1A regulator through
VIN/SW pair E, and Buck 4 operates as a 3A regulator
through VIN/SW pairs F, G, and H.
LTC3370
15
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For more information www.linear.com/LTC3370
operaTion
Table 1. Master Slave Program Combinations (Each Letter
Corresponds to a VIN and SW Pair)
PROGRAM
CODE
C3C2C1 BUCK 1 BUCK 2 BUCK 3 BUCK 4
000 AB CD EF GH
001 ABC D EF GH
010 ABC D E FGH
011 ABCH D E FG
100 ABC DE Not Used FGH
101 ABCD Not Used EF GH
110 ABCD Not Used E FGH
111 ABCD Not Used Not Used EFGH
Power Failure Reporting Via PGOODALL Pin
Power failure conditions are reported back by the
PGOODALL pin. Each buck switching regulator has an
internal power good (PGOOD) signal. When the regulated
output voltage of an enabled switcher falls below 98% for
Buck regulator 1 or 95% for Buck regulators 2-4 of its
programmed value, the PGOOD signal is pulled low. If any
PGOOD signal stays low for greater than 100µs, then the
PGOODALL pin is pulled low, indicating to a microprocessor
that a power failure fault has occurred. The 100µs filter time
prevents the pin from being pulled low due to a transient.
The PGOOD signal has a 0.3% hysteresis such that when
the regulated output voltage of an enabled switcher rises
above 98.3% or 95.3%, respectively, of its programmed
value, the PGOOD signal transitions high.
Temperature Monitoring and Overtemperature
Protection
To prevent thermal damage to the LTC3370 and its sur-
rounding components, the LTC3370 incorporates an
overtemperature (OT) function. When the LTC3370 die
temperature reaches 170°C (typical) all enabled buck
switching regulators are shut down and remain in shutdown
until the die temperature falls to 160°C (typical).
The temperature may be read back by the user by sampling
the TEMP pin analog voltage. The temperature, T, indicated
by the TEMP pin voltage is given by:
T=
V
TEMP
– 45mV
7mV
•1°C
(1)
If none of the buck switching regulators are enabled, then
the temperature monitor is also shut down to further
reduce quiescent current.
Programming the Operating Frequency
Selection of the operating frequency is a trade-off between
efficiency and component size. High frequency operation
allows the use of smaller inductor and capacitor values.
Operation at lower frequencies improves efficiency by
reducing internal gate charge losses but requires larger
inductance values and/or capacitance to maintain low
output voltage ripple.
The operating frequency for all of the LTC3370 regulators
is determined by an external resistor that is connected
between the RT pin and ground. The operating frequency
can be calculated using the following equation:
fOSC =8•1011 •ΩHz
R
T
(2)
While the LTC3370 is designed to function with operat-
ing frequencies between 1MHz and 3MHz, it has safety
clamps that will prevent the oscillator from running faster
than 4MHz (typical) or slower than 250kHz (typical). Tying
the RT pin to VCC sets the oscillator to the default internal
operating frequency of 2MHz (typical).
The LTC3370’s internal oscillator can be synchronized
through an internal PLL circuit to an external frequency
by applying a square wave clock signal to the PLL/MODE
pin. During synchronization, the top MOSFET turn-on of
Buck regulator 1 is phase locked to the rising edge of
the external frequency source. All other buck switching
regulators are locked to the appropriate phase of the ex-
ternal frequency source (see Buck Switching Regulators).
The synchronization frequency range is 1MHz to 3MHz.
A synchronization signal on the PLL/MODE pin will force
all active buck switching regulators to operate in forced
continuous mode PWM.
16
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For more information www.linear.com/LTC3370
applicaTions inForMaTion
Buck Switching Regulator Output Voltage and
Feedback Network
The output voltage of the buck switching regulators is
programmed by a resistor divider connected from the
switching regulator’s output to its feedback pin and is
given by VOUT = VFB(1 + R2/R1) as shown in Figure 1.
Typical values for R1 range from 40kΩ to 1MΩ. The buck
regulator transient response may improve with optional
capacitor, CFF, that helps cancel the pole created by the
feedback resistors and the input capacitance of the FB pin.
Experimentation with capacitor values between 2pF and
22pF may improve transient response.
the C1, C2, and C3 pins (see Table 1). Tables 3, 4, and 5
show recommended inductors for the combined power
stage configurations.
The input supply should be decoupled with a 22µF capacitor
while the output should be decoupled with a 47µF capaci-
tor for a 2A combined buck regulator. Likewise for 3A and
4A configurations the input and output capacitance must
be scaled up to account for the increased load. Refer to
the Capacitor Selection section for details on selecting a
proper capacitor.
In some cases it may be beneficial to use more power
stages than needed to achieve increased efficiency of the
active regulators. In general the efficiency will improve by
adding stages for any regulator running close to what the
rated load current would be without the additional stage.
For example, if the application requires a 1A regulator that
supplies close to 1A at a high duty cycle, a 3A regulator
that only peaks at 3A but averages a lower current, and
a 2A regulator that runs at 1.5A at a high duty cycle, bet-
ter efficiency may be achieved by using the 3A, 3A, 2A
configuration.
Input and Output Decoupling Capacitor Selection
The LTC3370 has individual input supply pins for each
buck power stage and a separate VCC pin that supplies
power to all top level control and logic. Each of these
pins must be decoupled with low ESR capacitors to GND.
These capacitors must be placed as close to the pins as
possible. Ceramic dielectric capacitors are a good compro-
mise between high dielectric constant and stability versus
temperature and DC bias. Note that the capacitance of a
capacitor deteriorates at higher DC bias. It is important
to consult manufacturer data sheets and obtain the true
capacitance of a capacitor at the DC bias voltage that it
will be operated at. For this reason, avoid the use of Y5V
dielectric capacitors. The X5R/X7R dielectric capacitors
offer good overall performance.
The input supply voltage Pins 1, 4, 5, 8, 17, 20, 21, 24 and
29 all need to be decoupled with at least 10µF capacitors. If
power stages are combined the supplies should be shorted
with as short of a trace as possible, and the decoupling
capacitor should be scaled accordingly.
+
BUCK
SWITCHING
REGULATOR
VOUT
FB
R1
3370 F01
R2
CFF
OPTIONAL
COUT
Figure 1. Feedback Components
Buck Regulators
All four buck regulators are designed to be used with
inductors ranging from 1µH to 3.3µH depending on the
lowest switching frequency at which the buck regulator
must operate. When operating at 1MHz a 3.3µH inductor
should be used, while at 3MHz a 1µH inductor may be
used, or a higher value inductor may be used if reduced
current ripple is desired. Table 2 shows some recom-
mended inductors for the buck regulators. The bucks are
compensated to operate across the range of possible VIN
and VOUT voltages when the appropriate inductance is
used for the desired switching frequency.
The input supply should be decoupled with a 10µF capacitor
while the output should be decoupled with a 22µF capaci-
tor. Refer to the Capacitor Selection section for details on
selecting a proper capacitor.
Combined Buck Power Stages
The LTC3370 has eight power stages that can handle aver-
age load currents of 1A each. These power stages may be
combined in any one of eight possible combinations, via
LTC3370
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For more information www.linear.com/LTC3370
applicaTions inForMaTion
Table 2. Recommended Inductors for 1A Buck Regulators
PART NUMBER L (µH) MAX IDC (A) MAX DCR (mΩ) SIZE IN mm (L × W × H) MANUFACTURER
IHLP1212ABER1R0M-11 1.0 3 38 3 × 3.6 × 1.2 Vishay
1239AS-H-1R0N 1 2.5 65 2.5 × 2.0 × 1.2 Toko
XFL4020-222ME 2.2 3.5 23.5 4 × 4 × 2.1 CoilCraft
1277AS-H-2R2N 2.2 2.6 84 3.2 × 2.5 × 1.2 Toko
IHLP1212BZER2R2M-11 2.2 3 46 3 × 3.6 × 1.2 Vishay
XFL4020-332ME 3.3 2.8 38.3 4 × 4 × 2.1 CoilCraft
IHLP1212BZER3R3M-11 3.3 2.7 61 3 × 3.6 × 1.2 Vishay
Table 3. Recommended Inductors for 2A Buck Regulators
PART NUMBER L (µH) MAX IDC (A) MAX DCR (mΩ) SIZE IN mm (L × W × H) MANUFACTURER
XFL4020-102ME 1.0 5.1 11.9 4 × 4 × 2.1 CoilCraft
74437324010 1 5 27 4.45 × 4.06 × 1.8 Würth Elektronik
XAL4020-222ME 2.2 5.6 38.7 4 × 4 × 2.1 CoilCraft
FDV0530-2R2M 2.2 5.3 15.5 6.2 × 5.8 × 3 Toko
IHLP2020BZER2R2M-11 2.2 5 37.7 5.49 × 5.18 × 2 Vishay
XAL4030-332ME 3.3 5.5 28.6 4 × 4 × 3.1 CoilCraft
FDV0530-3R3M 3.3 4.1 34.1 6.2 × 5.8 × 3 Toko
Table 4. Recommended Inductors for 3A Buck Regulators
PART NUMBER L (µH) MAX IDC (A) MAX DCR (mΩ) SIZE IN mm (L × W × H) MANUFACTURER
XAL4020-102ME 1.0 8.7 14.6 4 × 4 × 2.1 CoilCraft
FDV0530-1R0M 1 8.4 11.2 6.2 × 5.8 × 3 Toko
XAL5030-222ME 2.2 9.2 14.5 5.28 × 5.48 × 3.1 CoilCraft
IHLP2525CZER2R2M-01 2.2 8 20 6.86 × 6.47 × 3 Vishay
74437346022 2.2 6.5 20 7.3 × 6.6 × 2.8 Würth Elektronik
XAL5030-332ME 3.3 8.7 23.3 5.28 × 5.48 × 3.1 CoilCraft
SPM6530T-3R3M 3.3 7.3 27 7.1 × 6.5 × 3 TDK
Table 5. Recommended Inductors for 4A Buck Regulators
PART NUMBER L (µH) MAX IDC (A) MAX DCR (mΩ) SIZE IN mm (L × W × H) MANUFACTURER
XAL5030-122ME 1.2 12.5 9.4 5.28 × 5.48 × 3.1 CoilCraft
SPM6530T-1R0M120 1 14.1 7.81 7.1 × 6.5 × 3 TDK
XAL5030-222ME 2.2 9.2 14.5 5.28 × 5.48 × 3.1 CoilCraft
SPM6530T-2R2M 2.2 8.4 19 7.1 × 6.5 × 3 TDK
IHLP2525EZER2R2M-01 2.2 13.6 20.9 6.86 × 6.47 × 5 Vishay
XAL6030-332ME 3.3 8 20.81 6.36 × 6.56 × 3.1 CoilCraft
FDVE1040-3R3M 3.3 9.8 10.1 11.2 × 10 × 4 Toko
LTC3370
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For more information www.linear.com/LTC3370
applicaTions inForMaTion
PCB Considerations
When laying out the printed circuit board, the following
list should be followed to ensure proper operation of the
LTC3370:
1. The exposed pad of the package (Pin 33) should connect
directly to a large ground plane to minimize thermal and
electrical impedance.
2. Each of the input supply pins should have a decoupling
capacitor.
3. The connections to the switching regulator input supply
pins and their respective decoupling capacitors should
be kept as short as possible. The GND side of these
capacitors should connect directly to the ground plane
of the part. These capacitors provide the AC current
to the internal power MOSFETs and their drivers. It is
important to minimize inductance from these capacitors
to the VIN pins of the LTC3370.
4. The switching power traces connecting SWA, SWB,
SWC, SWD, SWE, SWF, SWG, and SWH to the induc-
tors should be minimized to reduce radiated EMI and
parasitic coupling. Due to the large voltage swing of
the switching nodes, high input impedance sensitive
nodes, such as the feedback nodes, should be kept far
away or shielded from the switching nodes or poor
performance could result.
5. The GND side of the switching regulator output capaci-
tors should connect directly to the thermal ground plane
of the part. Minimize the trace length from the output
capacitor to the inductor(s)/pin(s).
6. In a multiple power stage buck regulator application
the trace length of switch nodes to the inductor must
be kept equal to ensure proper operation.
7. Care should be taken to minimize capacitance on the
TEMP pin. If the TEMP voltage must drive more than
~30pF, then the pin should be isolated with a resistor
placed close to the pin of a value between 10k and 100k.
Keep in mind that any load on the isolation resistor will
create a proportional error.
LTC3370
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For more information www.linear.com/LTC3370
Typical applicaTions
4 × 2A Quad Buck Application
LTC3370
EXPOSED PAD
2.2µH
VINA
VINB
SWA
SWB
FB1
VING
VINH
SWG
SWH
FB4
VINC
VIND
SWC
SWD
FB2
VINE
VINF
SWE
SWF
FB3
3370 TA02
2.2µH
806k
649k
232k
464k
22µF
2.25V TO 5.5V
1.8V
2A
1.2V
2A 47µF 47µF
22µF
2.25V TO 5.5V
402k
RT
EN1
EN2
EN3
EN4
PLL/MODE
C1
C2
C3
VCC
PGOODALL
TEMP
MICROPROCESSOR
CONTROL
2.7V TO 5.5V
MICROPROCESSOR
CONTROL
10µF
2.2µH2.2µH
511k
162k
665k
309k
22µF
2.5V TO 5.5V
3.3V
2A
2.5V
2A 47µF 47µF
22µF
3.3V TO 5.5V
LTC3370
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For more information www.linear.com/LTC3370
Typical applicaTions
Buck Regulators with Sequenced Start-Up Driven from a High Voltage Upstream Buck Converter
EXPOSED PAD
2.2µH
VINH
VINA
VINB
VINC
SWH
SWA
SWB
SWC
FB1
VINF
VING
SWF
SWG
FB4
3370 TA03
2.2µH
806k
649k
232k
1M
464k
47µF
1.2V
4A
2.5V
1A
1.8V
2A
10µF 10µF
22µF
22µF
3.3V
1A
47µF
22µF
100µF
2.2µH
LTC3370
VIND
SWD
FB2
VINE
SWE
FB3
2.2µH
511k
162k
665k
309k
402k
RT
EN1
EN2
EN3
EN4
PLL/MODE
C1
C2
C3
VCC
PGOODALL
TEMP
VCC
MICROPROCESSOR
CONTROL
10µF
0.1µF
CIN
22µF
VIN
5.5V TO 36V
INTVCC
34.8k
470pF
100k
100k
COUT: SANYO 10TPE330M
D1: DFLS1100
L1 COILCRAFT SER1360-802KL
MTOP, MBOT: Si7850DP
19.1k
2.2µF
D1
0.1µF
FREQ
ITH
SGND
SGND
LTC3891
VIN
PGOOD
PLLIN/MODE
ILIM
INTVCC
PGND
L1
8µH RSENSE
7mΩ
BOOST
SW
BG
SENSE+
SENSE–
EXTVCC
VFB
TG MTOP
MBOT
1nF
COUT
330µF
5V
6A
TRACK/SS
RUN
VIN EN
KILL
INT
PB
TMR GND ON
LTC2955TS8-1
MICROPROCESSOR
CONTROL
MICROPROCESSOR
CONTROL
LTC3370
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For more information www.linear.com/LTC3370
Typical applicaTions
Combined Buck Regulators with Common Input Supply
LTC3370
EXPOSED PAD
2.2µH
VINA
SWA
SWB
SWC
SWD
FB1
VINH
SWH
SWG
SWF
FB4
3370 TA04
2.2µH
511k
511k
324k
649k
1.6V
3A
1.2V
4A
2.7V TO 5.5V
100µF 68µF
10µF10µF
10µF
10µF
10µF
10µF
10µF
10µF
VINB VING
VINC VINF
2.2µH
VIND
RT
FB2
EN2
C1
C2
C3
EN1
EN3
EN4
PLL/MODE
VINE
SWE
FB3
PGOODALL
TEMP
VCC
MICROPROCESSOR
CONTROL
665k
309k
2.5V
1A
22µF
10µF
MICROPROCESSOR
CONTROL
LTC3370
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For more information www.linear.com/LTC3370
package DescripTion
5.00 ±0.10
(4 SIDES)
NOTE:
1. DRAWING PROPOSED TO BE A JEDEC PACKAGE OUTLINE
M0-220 VARIATION WHHD-(X) (TO BE APPROVED)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
PIN 1
TOP MARK
(NOTE 6)
0.40 ±0.10
31
1
2
32
BOTTOM VIEW—EXPOSED PAD
3.50 REF
(4-SIDES)
3.45 ±0.10
3.45 ±0.10
0.75 ±0.05 R = 0.115
TYP
0.25 ±0.05
(UH32) QFN 0406 REV D
0.50 BSC
0.200 REF
0.00 – 0.05
0.70 ±0.05
3.50 REF
(4 SIDES)
4.10 ±0.05
5.50 ±0.05
0.25 ±0.05
PACKAGE OUTLINE
0.50 BSC
RECOMMENDED SOLDER PAD LAYOUT
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
PIN 1 NOTCH R = 0.30 TYP
OR 0.35 × 45° CHAMFER
R = 0.05
TYP
3.45 ±0.05
3.45 ±0.05
UH Package
32-Lead Plastic QFN (5mm × 5mm)
(Reference LTC DWG # 05-08-1693 Rev D)
Please refer to http://www.linear.com/product/LTC3370#packaging for the most recent package drawings.
LTC3370
23
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For more information www.linear.com/LTC3370
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
revision hisTory
REV DATE DESCRIPTION PAGE NUMBER
A 03/16 Changed pin labeling on Typical Application circuit 1
B 09/16 Changed Pin Configuration TJMAX to 150°C 3
LTC3370
24
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For more information www.linear.com/LTC3370
LINEAR TECHNOLOGY CORPORATION 2015
LT 0916 REV B • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC3370
relaTeD parTs
Typical applicaTion
Combined Bucks with 3MHz Switching Frequency and Sequenced Power Up
PART NUMBER DESCRIPTION COMMENTS
LTC3589 8-Output Regulator with Sequencing and I2C Triple I2C Adjustable High Efficiency Step-Down DC/DC Converters: 1.6A, 1A, 1A.
High Efficiency 1.2A Buck-Boost DC/DC Converter, Triple 250mA LDO Regulators.
Pushbutton On/Off Control with System Reset, Flexible Pin-Strap Sequencing
Operation. I2C and Independent Enable Control Pins, Dynamic Voltage Scaling and
Slew Rate Control. Selectable 2.25MHz or 1.12MHz Switching Frequency, 8µA
Standby Current, 40-Lead (6mm × 6mm × 0.75mm) QFN.
LTC3675 7-Channel Configurable High Power PMIC Quad Synchronous Buck Regulators (1A, 1A, 500mA, 500mA). Buck DC/DCs Can be
Paralleled to Deliver Up to 2× Current with a Single Inductor. 1A Boost, 1A Buck-
Boost, 40V LED Driver. 44-Lead (4mm × 7mm × 0.75mm) QFN Package.
LTC3676 8-Channel Power Management Solution for
Application Processor
Quad Synchronous Buck Regulators (2.5A, 2.5A, 1.5A, 1.5A). Quad LDO Regulators
(300mA, 300mA, 300mA, 25mA). Pushbutton On/Off Control with System Reset.
DDR Solution with VTT and VTTR Reference. 40-Lead (6mm × 6mm × 0.75mm) QFN
Package.
LTC3375
LTC3374
8-Channel Programmable Configurable
1A DC/DC
8 × 1A Synchronous Buck Regulators. Can Connect Up to Four Power Stages in
Parallel to Make a Single Inductor, High Current Output (4A Maximum), 15 Output
Configurations Possible, 48-Lead (7mm × 7mm × 0.75mm) QFN Package (LTC3375)
38-Lead (5mm × 7mm × 0.75mm) QFN and TSSOP Packages (LTC3374).
LTC3371 4-Channel Configurable DC/DC with 8 × 1A
Power Stages
4 Synchronous Buck Regulators with 8 × 1A Power Stages. Can Connect Up to
Four Power Stages in Parallel to Make a Single Inductor, High Current Output (4A
Maximum), 8 Output Configurations Possible, Precision RST Monitoring with
Windowed Watchdog Timer (CT Programmable), 38-Lead (5mm × 7mm × 0.75mm)
QFN and TSSOP Packages.
LTC3370
EXPOSED PAD
1µH
SWA
SWB
SWC
FB1
VINC
VINB
VINA
VING
VINH
SWH
SWG
FB4
3370 TA05
1µH
649k
432k
324k
649k
2V
2A
2.25V TO 5.5V
2.5V TO 5.5V
1.2V
3A
2.25V TO 5.5V
68µF
10µF
10µF
10µF
10µF
10µF
47µF
1µH
C1
C2
C3
TEMP
PLL/MODE
EN1
EN2
EN3
EN4
SWE
SWF
FB3
PGOODALL
SWD
VIND VINE
VINF
FB2
511k
162k
RT
VCC
VCC
MICROPROCESSOR
CONTROL
1µH
665k
309k
2.7V TO 5.5V
47µF
10µF
10µF
22µF
10µF
10µF
2.5V
2A
3.3V
1A
3.3V TO 5.5V
267k
MICROPROCESSOR
CONTROL