LTC3728_15 Datasheet, PDF (1/36 Pages) Linear Technology – Dual, 550kHz, 2-Phase Synchronous Step-Down Switching Regulator

FEATURES
n _{Dual, 180° Phased Controllers Reduce Required}
Input Capacitance and Power Supply Induced Noise
n _OPTI-LOOP^® _{Compensation Minimizes COUT}
n _{±1% Output Voltage Accuracy}
n _{Power Good Output Voltage Indicator}
n _{Phase-Lockable Fixed Frequency 250kHz to 550kHz}
n _{Dual N-Channel MOSFET Synchronous Drive}
n _{Wide VIN Range: 3.5V to 36V Operation}
n _{Very Low Dropout Operation: 99% Duty Cycle}
n _{Adjustable Soft-Start Current Ramping}
n _{Foldback Output Current Limiting}
n _{Latched Short-Circuit Shutdown with Defeat Option}
n _{Output Overvoltage Protection}
n _{Remote Output Voltage Sense}
n _{Low Shutdown IQ: 20μA}
n _{5V and 3.3V Regulators}
n _{3 Selectable Operating Modes: Constant-Frequency,}
Burst Mode^® Operation and PWM
n _{Available in 32-Pin 5mm × 5mm QFN and}
28-Pin SSOP Packages
APPLICATIONS
n _{Notebook and Palmtop Computers}
n _{Telecom Systems}
n _{Portable Instruments}
n _{Battery-Operated Digital Devices}
n _{DC Power Distribution Systems}
LTC3728
Dual, 550kHz, 2-Phase
Synchronous Step-Down
Switching Regulator
DESCRIPTION
The LTC^®3728 is a dual high performance step-down
switching regulator controller that drives all N-channel
synchronous power MOSFET stages. A constant-frequency
current mode architecture allows phase-lockable frequency
of up to 550kHz. 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 (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 V_OUT 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 LTC3728 includes a power good
output pin that indicates when both outputs are within
7.5% of their designed set point.
L, LT, LTC, LTM, Linear Technology, the Linear logo, 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, 5929620, 6177787,
6144194, 6100678, 5408150, 6580258, 5705919.
TYPICAL APPLICATION
4.7μF ⁺
M1
D3
V_IN PGOOD INTV_CC
D4
1μF
TG1
TG2
V_IN
C_IN 5.2V TO 28V
22μF
M2
50V
L1
3.2μH
C_B1, 0.1μF
f_IN
500kHz
BOOST1
BOOST2
SW1
SW2
LTC3728
BG1
BG2
PLLIN
PGND
C_B2, 0.1μF
L2
3.2μH
R_SENSE1
0.01Ω
V_OUT1
5V
R2
5A ₊
C_OUT1 105k
47μF 1%
R1
6V
20k
SP
1%
1000pF
C_C1
220pF
R_C1
15k
SENSE1⁺
SENSE2⁺
SENSE1^–
SENSE2^–
V_OSENSE1
I_TH1
V_OSENSE2
I_TH2
RUN/SS1 SGND RUN/SS2
C_SS1
0.1μF
C_SS2
0.1μF
1000pF
C_C2
220pF
R_C2
15k
R_SENSE2
0.01Ω
R4
63.4k C_OUT
R3
1% 56μF
20k
6V
1%
SP
V_OUT2
3.3V
5A
M1, M2: FDS6982S
3728 F01
Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter
3728fg
1