LTC1628-SYNC
High Efficiency, 2-Phase
Synchronous Step-Down Switching Regulator
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FEATURES
DESCRIPTIO
The LTC®1628-SYNC is a high performance dual step-
down switching regulator controller that drives all
N-channel synchronous power MOSFET stages. A con-
stant frequency current mode architecture allows phase-
lockable frequency of up to 300kHz. Power loss and noise
due to the ESR of the input capacitors are minimized by
operating the two controller output stages out of phase.
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Out-of-Phase Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
OPTI-LOOPTM Compensation Minimizes COUT
Dual N-Channel MOSFET Synchronous Drive
±1% Output Voltage Accuracy
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Power Good Output Voltage Monitor
Phase-Lockable Fixed Frequency 150kHz to 300kHz
Wide VIN Range: 3.5V to 36V Operation
Very Low Dropout Operation: 99% Duty Cycle
Adjustable Soft-Start Current Ramping
Foldback Output Current Limiting
Latched Short-Circuit Shutdown with Defeat Option
Output Overvoltage Protection
OPTI-LOOP compensation allows the transient response
tobeoptimizedoverawiderangeofoutputcapacitanceand
ESRvalues. Theprecision0.8Vreferenceandpowergood
output indicator are compatible with future microproces-
sor generations, and a wide 3.5V to 30V (36V maximum)
input supply range encompasses all battery chemistries.
Remote Output Voltage Sense
A RUN/SS pin for each controller provides both soft-start
and optional timed, short-circuit shutdown. Current
foldback limits MOSFET dissipation during short-circuit
conditions when overcurrent latchoff is disabled. Output
overvoltage protection circuitry latches on the bottom
MOSFET until VOUT returns to normal. The FCB mode pin
can select among Burst Mode, constant frequency mode
and continuous inductor current mode or regulate a
secondarywinding. TheLTC1628-SYNCincludesapower
good output pin that indicates when both outputs are
within 7.5% of their designed set point.
Low Shutdown IQ: 20µA
5V and 3.3V Standby Regulators
Small 28-Lead SSOP Package
Selectable Constant Frequency or Burst ModeTM
Operation
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APPLICATIO S
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Notebook and Palmtop Computers, PDAs
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Telecom Systems
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Portable Instruments
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Battery-Operated Digital Devices
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation.
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DC Power Distribution Systems
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V
IN
5.2V TO 28V
TYPICAL APPLICATIO
C
IN
+
1µF
22µF
4.7µF
D3
CERAMIC
50V
D4
V
PGOOD INTV
IN
CC
CERAMIC
M1
M3
M4
TG1
TG2
L1
6.3µH
L2
6.3µH
C
, 0.1µF
B2
BOOST1
SW1
BOOST2
SW2
LTC1628-SYNC
C
, 0.1µF
B1
M2
BG1
BG2
D1
D2
f
PLLIN
SENSE1
PGND
IN
+
+
SENSE2
R
R
SENSE2
0.01Ω
SENSE1
1000pF
1000pF
0.01Ω
–
–
SENSE1
SENSE2
V
V
3.3V
5A
OUT1
5V
5A
OUT2
V
V
OSENSE2
OSENSE1
R2
105k
1%
R4
63.4k
1%
I
I
TH1
TH2
C
C
C2
C
C1
220pF
C
56µF
6V
OUT1
OUT
RUN/SS1
SGND
RUN/SS2
+
+
R1
20k
1%
R3
20k
1%
220pF
R
C2
47µF
6V
R
C1
C
C
SS1
0.1µF
SS2
0.1µF
15k
15k
SP
SP
M1, M2, M3, M4: FDS6680A
1628 F01
Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter
1