LTC3707 Datasheet, PDF (1/32 Pages) Linear Technology – High Effi ciency, 2-Phase Synchronous Step-Down Switching Regulator

FEATURES
■ _{180° Phased Dual Controllers Reduce Required}
Input Capacitance and Power Supply Induced Noise
■ _OPTI-LOOP^® _{Compensation Minimizes COUT}
■ _{±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 VIN 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 IQ: 20μA}
■ _{5V and 3.3V Standby Regulators}
■ _{Selectable Constant Frequency, Burst Mode}^®
Operation or PWM Operation
■ _{Small 28-Lead Narrow SSOP Package}
APPLICATIONS
■ _{Notebook and Palmtop Computers, PDAs}
■ _{Battery Chargers}
■ _{Portable Instruments}
■ _{Battery-Operated Digital Devices}
■ _{DC Power Distribution Systems}
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.
TYPICAL APPLICATION
M1
L1
6.3μH
D1
M2
R_SENSE1
0.01Ω
V_OUT1
5V
5A
R2
105k
+
C_OUT1
47μF
1%
6V
SP
R1
20k
1%
+
4.7μF
C_B1, 0.1μF
D3
V_IN
TG1
INTV_CC
TG2
BOOST1
BOOST2
SW1
SW2
LTC3707
BG1
BG2
1000pF
C_C1
220pF
R_C1
15k
SGND
SENSE1⁺
PGND
SENSE2⁺
SENSE1^–
V_OSENSE1
I_TH1
RUN/SS1
C_SS1
0.1μF
SENSE2^–
V_OSENSE2
I_TH2
RUN/SS2
C_SS2
0.1μF
1μF
D4
CERAMIC
M3
C_B2, 0.1μF
M4
1000pF
C_C2
220pF
R3
R_C2
15k
20k
1%
V_IN
C_IN ^{5.2V TO 28V}
22μF
50V
CERAMIC
L2
6.3μH
D2
R_SENSE2
0.01Ω
R4
63.4k
1%
C_OUT
56μF
6V
SP
V_OUT2
3.3V
5A
M1, M2, M3, M4: FDS6680A
3707 F01
Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter
3707fb
1