FEATURES
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LTC3707
High Efficiency, 2-Phase
Synchronous Step-Down
Switching Regulator
DESCRIPTION
The LTC
®
3707 is a high performance dual step-down
switching regulator controller that drives 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.
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 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 V
OUT
returns to normal. The FCB mode
pin can select among Burst Mode operation, constant
frequency mode and continuous inductor current mode
or regulate a secondary winding.
L,
LT, LTC, LTM, Burst Mode, and OPTI-LOOP are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners. Protected by U.S.
Patents including 5481178, 5705919, 5929620, 6144194, 6177787, 6304066, 6580258.
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180° Phased Dual Controllers Reduce Required
Input Capacitance and Power Supply Induced Noise
OPTI-LOOP
®
Compensation Minimizes C
OUT
±1.5%
Output Voltage Accuracy over Temperature
Dual N-Channel MOSFET Synchronous Drive
Power Good Output Voltage Monitor
DC Programmed Fixed Frequency 150kHz to 300kHz
Wide V
IN
Range: 4.5V to 28V 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 I
Q
: 20μA
5V and 3.3V Standby Regulators
Selectable Constant Frequency, Burst Mode
®
Operation or PWM Operation
Small 28-Lead Narrow SSOP Package
Notebook and Palmtop Computers, PDAs
Battery Chargers
Portable Instruments
Battery-Operated Digital Devices
DC Power Distribution Systems
APPLICATIONS
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TYPICAL APPLICATION
M1
L1
6.3μH
+
4.7μF
D3
V
IN
TG1
C
B1
, 0.1μF
BOOST1
SW1
INTV
CC
TG2
BOOST2
SW2
LTC3707
BG2
PGND
SENSE2
+
1000pF
SENSE1
–
V
OSENSE1
SENSE2
–
V
OSENSE2
I
TH2
RUN/SS2
C
SS2
0.1μF
C
C2
220pF
R
C2
15k
D4
1μF
CERAMIC
M3
C
B2
, 0.1μF
V
IN
5.2V TO 28V
C
IN
22μF
50V
CERAMIC
L2
6.3μH
D1
M2
BG1
SGND
M4
D2
SENSE1
+
R
SENSE1
0.01Ω
V
OUT1
5V
5A
1000pF
R
SENSE2
0.01Ω
V
OUT2
3.3V
5A
C
OUT
56μF
6V
SP
+
C
OUT1
47μF
6V
SP
R2
105k
1%
R1
20k
1%
C
C1
220pF
R
C1
15k
I
TH1
RUN/SS1
C
SS1
0.1μF
R3
20k
1%
R4
63.4k
1%
+
M1, M2, M3, M4: FDS6680A
3707 F01
Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter
3707fb
1
LINER [ LINEAR TECHNOLOGY ]
