LTC1628/LTC1628-PG
High Efficiency, 2-Phase
Synchronous Step-Down Switching Regulators
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FEATURES
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DESCRIPTIO
The LTC®1628/LTC1628-PG are high performance dual
step-down switching regulator controllers that drive all
N-channel synchronous power MOSFET stages. A constant frequency current mode architecture allows adjustment of the frequency 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.
Out-of-Phase Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
OPTI-LOOP® Compensation Minimizes COUT
±1% Output Voltage Accuracy
Dual N-Channel MOSFET Synchronous Drive
Power Good Output Voltage Monitor (LTC1628-PG)
DC Programmed 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
Remote Output Voltage Sense
Low Shutdown IQ: 20µA
5V and 3.3V Standby Regulators
Selectable Constant Frequency or Burst Mode®
Operation
Available in 5mm × 5mm QFN and
28-Pin SSOP Packages
OPTI-LOOP compensation allows the transient response
to be optimized over a wide range of output capacitance and
ESR values. The precision 0.8V reference and power good
output indicator are compatible with future microprocessor generations, and a wide 3.5V to 30V (36V maximum)
input supply range encompasses all battery chemistries.
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
secondary winding. The LTC1628-PG includes a power
good output pin that replaces the FLTCPL, fault coupling
control pin of the LTC1628.
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APPLICATIO S
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Notebook and Palmtop Computers, PDAs
Battery Chargers
Portable Instruments
Battery-Operated Digital Devices
DC Power Distribution Systems
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TYPICAL APPLICATIO
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP and Burst Mode are registered trademarks of Linear Technology Corporation.
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4.7µF
D3
VIN
M1
L1
6.3µH
CB1, 0.1µF
BOOST1
BG1
BOOST2
+
COUT1
47µF
6V
SP
R1
20k
1%
CC1
220pF
RC1
15k
M4
D2
PGND
SENSE2 +
SENSE1–
VOSENSE1
ITH1
SENSE2 –
VOSENSE2
ITH2
1000pF
R2
105k
1%
L2
6.3µH
CB2, 0.1µF
BG2
SENSE1+
VOUT1
5V
5A
VIN
5.2V TO 28V
CIN
22µF
50V
CERAMIC
SW2
LTC1628
SGND
RSENSE1
0.01Ω
M3
TG2
SW1
M2
D1
D4
INTVCC
TG1
1µF
CERAMIC
RSENSE2
0.01Ω
1000pF
RUN/SS1
CSS1
0.1µF
RUN/SS2
CSS2
0.1µF
CC2
220pF
RC2
15k
R3
20k
1%
M1, M2, M3, M4: FDS6680A
R4
63.4k
1%
VOUT2
3.3V
5A
COUT
56µF
6V
SP
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1628 F01
Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter
1628fb
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