LTC3735
2-Phase, High Efficiency
DC/DC Controller for
Intel Mobile CPUs
FEATURES
DESCRIPTION
The LTC®3735 is a 2-phase synchronous step-down
switching regulator controller that drives all N-channel
power MOSFETs in a constant frequency architecture. The
output voltage is programmable by six VID bits during
normal operation and by external resistors during initial
boot-upanddeepersleepstate.TheLTC3735drivesitstwo
output stages out-of-phase at frequencies up to 550kHz
to minimize the RMS ripple currents in both input and
output capacitors. This antiphase technique also doubles
the apparent switching frequency, improving the transient
response while operating each phase at an optimum fre-
quency for efficiency. Thermal design is further simplified
bycycle-by-cyclecurrentsharingbetweenthetwophases.
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Output Stages Operate Antiphase
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1ꢀ Output ꢁoltage Accuracy
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6-Bit IMꢁP-Iꢁ ꢁID Code: ꢁ
= 0.7ꢁ to 1.708ꢁ
OUT
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Intel Compatible Power Saving Mode (PSIB)
Stage Shedding Improves Low Current Efficiency
Power Good Output with Adaptive Masking
Lossless ꢁoltage Positioning
Dual Input Supply Capability for Load Sharing
Resistor Programmable V
Sleep State
at Boot-Up and Deeper
OUT
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Resistor Programmable Deep Sleep Offset
Programmable Fixed Frequency: 210kHz to 550kHz
Adjustable Soft-Start Current Ramping
Foldback Output Current Limit
Short-Circuit Shutdown Timer with Defeat Option
Overvoltage Protection
AnIntelcompatiblePSIBinputisprovidedtoselectbetween
two modes of operation. Fully enhanced synchronous
mode achieves a very small output ripple and very fast
transient response while power saving mode realizes
very high efficiency. OPTI-LOOP® compensation allows
the transient response to be optimized for a wide range
of output capacitance and ESR values.
Available in 36-Lead SSOP (0.209 Wide) and 38-Lead
(5mm × 7mm) Packages
APPLICATIONS
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Mobile and Desktop Computers
Internet Servers
L, LT, LTC, LTM, OPTI-LOOP, PolyPhase, Linear Technology and the Linear logo are registered
trademarks of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
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TYPICAL APPLICATION
M1
M2
MCH_PG
DPRSLPVR
STP_CPUB
PSIB
TG1
SW1
1µH
D1
0.002Ω
0.002Ω
V
IN
5V TO 24V
BG1
FREQSET
PGND
VID5-VID0
V
OUT
+
–
0.7V TO 1.708V
40A
PGOOD SENSE1
SENSE1
C
C
IN
OUT
+
I
TH
330µF
2V
10µF
35V
×4
R
C
100pF
RUN/SS
M3
M4
TG2
SW2
BG2
4.74k
1µH
D2
×5
232k
C
C
0.1µF
470pF
SGND
+
V
OA
LTC3735
+
–
SENSE2
SENSE2
4.5V TO 7V
PV
CC
13.3k
V
4.7µF
12.7k
RBOOT
BAT54A
56.2k
13.3k
BOOST1 RDPRSLP
1.27M
549k
BOOST2
RDPSLP
+
0.47µF
0.47µF
+
V
OA
OA
OAOUT
–
SW2
SW1
V
OA
3735 F01
Figure 1. High Current 2-Phase Step-Down Converter
3735fa
1