LTC3731
3-Phase, 600kHz,
Synchronous Buck Switching
Regulator Controller
FEATURES DESCRIPTION
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3-Phase Current Mode Controller with Onboard
The LTC 3731 is a PolyPhase synchronous step-down
MOSFET Drivers
switching regulator controller that drives all N-channel
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5% Output Current Matching Optimizes Thermal
external power MOSFET stages in a phase-lockable fixed
Performance and Size of Inductors and MOSFETs frequency architecture. The 3-phase controller drives its
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Differential Amplifier Accurately Senses V output stages with 120 phase separation at frequencies
OUT
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1% V Accuracy Over Temperature of up to 600kHz per phase to minimize the RMS current
REF
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V Range: 0.6V to 5.5V without Diffamp losses in both the input and output filter capacitors. The
OUT
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3-phase technique effectively triples the fundamental fre-
V Range: 0.6V to (V 1.2V) with Diffamp
OUT CC
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quency, improving transient response while operating each
250kHz to 600kHz Per Phase, PLL, Fixed Frequency
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controller at an optimal frequency for efficiency and ease of
PWM, Stage Shedding or Burst Mode Operation
n thermal design. Light load efficiency is optimized by using a
OPTI-LOOP Compensation Minimizes C
OUT
n choice of output Stage Shedding or Burst Mode operation.
Adjustable Soft-Start Current Ramping
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Short-Circuit Shutdown Timer with Defeat Option
A differential amplifier provides true remote sensing of
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Overvoltage Soft Latch
both the high and low side of the output voltage at the
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Adjustable Undervoltage Lockout Threshold
point of load.
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Selectable Phase Output for Up to 12-Phase Operation
Soft-start and a defeatable, timed short-circuit shutdown
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Available in 5mm 5mm QFN and 36-Pin Narrow
protect the MOSFETs and the load. Current foldback
(0.209") SSOP Packages
provides protection for the external MOSFETs under
short-circuit or overload conditions.
APPLICATIONS
L, LT, LTC, LTM, Bust Mode, OPTI-LOOP, PolyPhase, Linear Technology and the Linear logo
are registered and Stage Shedding is a trademark of Linear Technology Corporation. All other
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Desktop Computers and Servers
trademarks are the property of their respective owners. Protected by U.S. Patents, including
5481178, 5929620, 6177787, 6144194, 6100678, 5408150, 6580258, 6462525, 630466,
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High Performance Notebook Computers
5705919.
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High Output Current DC/DC Power Supplies
TYPICAL APPLICATION
V
IN
V
CC 5V TO 28V
V TG1
CC
+
4.5V TO 7V 0.8H
0.003
LTC3731 22F
10F
SW1
35V
BOOST1
BG1
BOOST2
BOOST3
+
0.1F SENSE1
SENSE1
V
SW3 SW2 SW1
IN
TG2
0.8H
POWER GOOD INDICATOR PGOOD 0.003 V
OUT
SW2 1.35V
OPTIONAL SYNC IN PLLIN
55A
BG2
PLLFLTR
PGND
36k
V UVADJ
IN +
SENSE2
12k
680pF SENSE2
V
IN
I
TH TG3
0.8H
0.003
5k
RUN/SS
SW3
0.01F
SGND
BG3
EAIN
100pF
+
SENSE3
DIFFOUT
7.5k
SENSE3 +
IN C
OUT
+
IN 470F
6.04k
4V
3731 F01
Figure 1. High Current Triple Phase Step-Down Converter
3731fc
1LTC3731
ABSOLUTE MAXIMUM RATINGS (Note 1)
Topside Driver Voltages (BOOSTn) ............. 38V to 0.3V I Voltage ............................................... 2.4V to 0.3V
TH
Switch Voltage (SWn) ................................... 32V to 5V Operating Ambient Temperature Range
Boosted Driver Voltage (BOOSTn SWn) .... 7V to 0.3V LTC3731C ................................................ 0C to 70C
Peak Output Current < 1ms (TGn, BGn) ......................5A LTC3731I ..............................................40C to 85C
Supply Voltages (V , V ), PGOOD Junction Temperature (Note 2) ............................. 125C
CC DR
Pin Voltage ................................................... 7V to 0.3V Storage Temperature Range .................. 65C to 125C
RUN/SS, PLLFLTR, PLLIN, UVADJ, Lead Temperature G Package (Soldering, 10 sec)..300C
FCB Voltages ..............................................V to 0.3V Peak Body Temperature UH Package ................... 240C
CC
SENSE+, SENSE Voltages ....................... 5.5V to 0.3V
PIN CONFIGURATION
TOP VIEW
1 36 CLKOUT
V
CC
TOP VIEW
2 35 PGOOD
PLLIN
3 34 BOOST1
PLLFLTR
4 33 TG1
FCB
32 31 30 29 28 27 26 25
+
5 32 SW1
IN
IN 1 24 BOOST2
6 31 BOOST2
IN
DIFFOUT 2 23 TG2
7 30 TG2
DIFFOUT
EAIN SW2
3 22
+
8 29 SW2
EAIN
SENSE1 4 21 V
CC
33
SGND
9 28 V
SGND SENSE1 5 20 BG1
DR
+
+
10 27 BG1 SENSE2 6 19 PGND
SENSE1
SENSE2 7 18 BG2
11 26 PGND
SENSE1
+ SENSE3 8 17 BG3
12 25 BG2
SENSE2
9 10 11 12 13 14 15 16
13 24 BG3
SENSE2
14 23 SW3
SENSE3
+
15 22 TG3
SENSE3
16 21 BOOST3
RUN/SS
17 20 PHASMD
I UH PACKAGE
TH
32-LEAD (5mm 5mm) PLASTIC QFN
18 19 SGND2
UVADJ
T = 125C, = 34C/W
JMAX JA
EXPOSED PAD (PIN 33) IS SGND, MUST BE SOLDERED TO PCB
G PACKAGE
36-LEAD PLASTIC SSOP
T = 125C, = 95C/W, = 32C/W
JMAX JA JC
3731fc
2
+ +
SENSE3 IN
RUN/SS FCB
I PLLFLTR
TH
UVADJ PLLIN
PHASMD/PG CLKOUT
BOOST3 BOOST1
TG3 TG1
SW3 SW1