1
LTC3729
sn3729 3729fas
550kHz, PolyPhase,
High Efficiency, Synchronous
Step-Down Switching Regulator
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP is a registered trademark of Linear Technology Corporation.
PolyPhase is a trademark of Linear Technology Corporation.
The LTC
®
3729 is a multiple phase, synchronous step-
down current mode switching regulator controller that
drives N-channel external power MOSFET stages in a
phase-lockable fixed frequency architecture. The PolyPhase
controller drives its two output stages out of phase at
frequencies up to 550kHz to minimize the RMS ripple
currents in both input and output capacitors. The output
clock signal allows expansion for up to 12 evenly phased
controllers for systems requiring 15A to 200A of output
current. The multiple phase technique effectively multi-
plies the fundamental frequency by the number of chan-
nels used, improving transient response while operating
each channel at an optimum frequency for efficiency.
Thermal design is also simplified.
An internal differential amplifier provides true remote
sensing of the regulated supply’s positive and negative
output terminals as required for high current applications.
A RUN/SS pin provides both soft-start and optional timed,
short-circuit shutdown. Current foldback limits MOSFET
dissipation during short-circuit conditions when the
overcurrent latchoff is disabled. OPTI-LOOP compensa-
tion allows the transient response to be optimized over a
wide range of output capacitance and ESR values. The
LTC3729 includes a power good output pin that indicates
when the output is within
±
7.5% of the designed set point.
Figure 1. High Current Dual Phase Step-Down Converter
■
Desktop Computers/Servers
■
Large Memory Arrays
■
DC Power Distribution Systems
■
Wide V
IN
Range: 4V to 36V Operation
■
Reduces Required Input Capacitance and Power
Supply Induced Noise
■
±
1% Output Voltage Accuracy
■
Phase-Lockable Fixed Frequency: 250kHz to 550kHz
■
True Remote Sensing Differential Amplifier
■
PolyPhase
TM
Extends from Two to Twelve Phases
■
Reduces the Size and Value of Inductors
■
Current Mode Control Ensures Current Sharing
■
1.1MHz Effective Switching Frequency (2-Phase)
■
OPTI-LOOP
®
Compensation Reduces C
OUT
■
Power Good Output Voltage Indicator
■
Very Low Dropout Operation: 99% Duty Cycle
■
Adjustable Soft-Start Current Ramping
■
Internal Current Foldback Plus Shutdown Timer
■
Overvoltage Soft-Latch Eliminates Nuisance Trips
■
Available in 5mm
×
5mm QFN
and 28-Lead SSOP Packages
3729 TA01
TG1
BOOST1
SW1
BG1
PGND
SENSE1
+
SENSE1
–
TG2
BOOST2
SW2
BG2
INTV
CC
SENSE2
+
SENSE2
–
V
IN
RUN/SS
EAIN
I
TH
V
DIFFOUT
V
OS
–
V
OS
+
LTC3729
SGND
0.1
µ
F
PGOOD
0.1
µ
F
16k
1000pF
S
S
S
S
S
S
S
S
10
Ω
3.3k
16k
+
10
µ
F
35V
CERAMIC
×
4
+
C
OUT
1000
µ
F
×
2
4V
L1, L2: CEPH149-IROMC
C
OUT
: T510E108K004AS
D1, D2: UP5840
M1, M3: IRF7811W
M2, M4: IRF7822
V
OUT
1.6V/40A
L1
0.8
µ
H
0.002
Ω
V
IN
5V TO 28V
L2
0.8
µ
H
D2
D1
M1
M2
×
2
M3
M4
×
2
0.47
µ
F
S
0.47
µ
F
10
µ
F
0.002
Ω
APPLICATIO S
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FEATURES
TYPICAL APPLICATIO
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DESCRIPTIO
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