LTC3731
3-Phase, 600kHz,
Synchronous Buck Switching
Regulator Controller
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DESCRIPTIO
FEATURES
The LTC®3731 is a PolyPhase® synchronous step-down
switching regulator controller that drives all N-channel ex-
ternal power MOSFET stages in a phase-lockable fixed fre-
quency architecture. The 3-phase controller drives its
outputstageswith120°phaseseparationatfrequenciesof
upto600kHzperphasetominimizetheRMScurrentlosses
in both the input and output filter capacitors. The 3-phase
technique effectively triples the fundamental frequency,
improvingtransientresponsewhileoperatingeachcontrol-
ler at an optimal frequency for efficiency and ease of ther-
mal design. Light load efficiency is optimized by using a
choice of output Stage Shedding or Burst Mode operation.
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3-Phase Current Mode Controller with Onboard
MOSFET Drivers
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±5% Output Current Matching Optimizes Thermal
Performance and Size of Inductors and MOSFETs
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Differential Amplifier Accurately Senses VOUT
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±1% VREF Accuracy Over Temperature
Reduced Power Supply Induced Noise
±10% Power Good Output Indicator
250kHz to 600kHz Per Phase, PLL, Fixed Frequency
PWM, Stage SheddingTM or Burst Mode® Operation
OPTI-LOOP® Compensation Minimizes COUT
Adjustable Soft-Start Current Ramping
Short-Circuit Shutdown Timer with Defeat Option
Overvoltage Soft Latch
Adjustable Undervoltage Lockout Threshold
Selectable Phase Output for Up to 12-Phase Operation
Available in 5mm × 5mm QFN and 36-Pin Narrow
Adifferentialamplifierprovidestrueremotesensingofboth
the high and low side of the output voltage at the point of
load.Theprecisionreferencesupportsoutputvoltagesfrom
0.6V to 6V.
Soft-startandadefeatable, timedshort-circuitshutdown
protect the MOSFETs and the load. Current foldback
provides protection for the external MOSFETs under
(0.209") SSOP PUackages
APPLICATIO S
short-circuit or overload conditions.
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, LTC and LT are registered trademarks of Linear Technology Corporation.
Desktop Computers and Servers
Burst Mode, OPTI-LOOP and PolyPhase are registered trademarks of Linear Technology
Corporation. Stage Shedding is a trademark of Linear Technology Corporation.
*Protected by U.S. Patents including 5481178, 5929620, 6177787, 6144194, 6100678,
5408150, 6580258, 6462525, 6304066, 5705919.
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High Performance Notebook Computers
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High Output Current DC/DC Power Supplies
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TYPICAL APPLICATIO
V
IN
5V TO 28V
V
CC
V
TG1
SW1
BG1
CC
+
0.8µH
0.8µH
4.5V TO 7V
0.003Ω
0.003Ω
22µF
LTC3731
10µF
35V
BOOST1
BOOST2
BOOST3
+
SENSE1
0.1µF
–
SENSE1
V
V
SW3 SW2 SW1
IN
TG2
PGOOD
PLLIN
POWER GOOD INDICATOR
OPTIONAL SYNC IN
V
OUT
SW2
BG2
1.35V
55A
PLLFLTR
PGND
36k
V
IN
UVADJ
+
SENSE2
12k
–
680pF
SENSE2
IN
I
TH
TG3
SW3
BG3
0.8µH
0.003Ω
5k
RUN/SS
0.01µF
SGND
EAIN
100pF
7.5k
+
SENSE3
DIFFOUT
IN
IN
–
–
+
SENSE3
+
C
OUT
470µF
6.04k
4V
3731 F01
Figure 1. High Current Triple Phase Step-Down Converter
3731fa
1