LTC3731
1
3731fc
TYPICAL APPLICATION
FEATURES DESCRIPTION
3-Phase, 600kHz,
Synchronous Buck Switching
Regulator Controller
The LTC
®
3731 is a PolyPhase
®
synchronous step-down
switching regulator controller that drives all N-channel
external power MOSFET stages in a phase-lockable fixed
frequency architecture. The 3-phase controller drives its
output stages with 120° phase separation at frequencies
of up to 600kHz per phase to minimize the RMS current
losses in both the input and output filter capacitors. The
3-phase technique effectively triples the fundamental fre-
quency, improving transient response while operating each
controller at an optimal frequency for efficiency and ease of
thermal design. Light load efficiency is optimized by using a
choice of output Stage Shedding or Burst Mode operation.
A differential amplifier provides true remote sensing of
both the high and low side of the output voltage at the
point of load.
Soft-start and a defeatable, timed short-circuit shutdown
protect the MOSFETs and the load. Current foldback
provides protection for the external MOSFETs under
short-circuit or overload conditions.
APPLICATIONS
n
3-Phase Current Mode Controller with Onboard
MOSFET Drivers
n
±5% Output Current Matching Optimizes Thermal
Performance and Size of Inductors and MOSFETs
n
Differential Amplifier Accurately Senses V
OUT
n
±1% V
REF
Accuracy Over Temperature
n
V
OUT
Range: 0.6V to 5.5V without Diffamp
n
V
OUT
Range: 0.6V to (V
CC
– 1.2V) with Diffamp
n
250kHz to 600kHz Per Phase, PLL, Fixed Frequency
n
PWM, Stage Shedding™ or Burst Mode
®
Operation
n
OPTI-LOOP
®
Compensation Minimizes C
OUT
n
Adjustable Soft-Start Current Ramping
n
Short-Circuit Shutdown Timer with Defeat Option
n
Overvoltage Soft Latch
n
Adjustable Undervoltage Lockout Threshold
n
Selectable Phase Output for Up to 12-Phase Operation
n
Available in 5mm × 5mm QFN and 36-Pin Narrow
(0.209") SSOP Packages
n
Desktop Computers and Servers
n
High Performance Notebook Computers
n
High Output Current DC/DC Power Supplies
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
trademarks are the property of their respective owners. Protected by U.S. Patents, including
5481178, 5929620, 6177787, 6144194, 6100678, 5408150, 6580258, 6462525, 630466,
5705919.
Figure 1. High Current Triple Phase Step-Down Converter
V
IN
0.003Ω
0.8µH
22µF
35V
0.003Ω
0.8µH
V
IN
0.003Ω
C
OUT
470µF
4V
V
OUT
1.35V
55A
IN
5V TO 28V
0.8µH
V
IN
3731 F01
TG1V
CC
0.1µF
SW3 SW2 SW1
SW1
BG1
SENSE1
+
SENSE1
–
BOOST1
BOOST2
BOOST3
TG2
SW2
BG2
PGOOD
PLLIN
PLLFLTR
I
TH
0.01µF
680pF
5k
OPTIONAL SYNC IN
POWER GOOD INDICATOR
RUN/SS
SGND
EAIN
DIFFOUT
PGND
UVADJ
SENSE2
+
SENSE2
–
TG3
SW3
BG3
SENSE3
+
SENSE3
–
IN
–
IN
+
+
10µF
V
CC
4.5V TO 7V
+
LTC3731
36k
12k
7.5k
100pF
6.04k
