LTC3728 Datasheet, PDF (1/32 Pages) Linear Technology – Dual, 550kHz, 2-Phase Synchronous Step-Down Switching Regulator

LTC3728
Dual, 550kHz, 2-Phase
Synchronous Step-Down Switching Regulator
FEATURES
DESCRIPTIO
■ _{Dual, 180° Phased Controllers Reduce Required}
Input Capacitance and Power Supply Induced Noise
■ _OPTI-LOOP^® _{Compensation Minimizes COUT}
■ _{±1% Output Voltage Accuracy}
■ _{Power Good Output Voltage Indicator}
■ _{Phase-Lockable Fixed Frequency 250kHz to 550kHz}
■ _{Dual N-Channel MOSFET Synchronous Drive}
■ _{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 Regulators}
■ _{3 Selectable Operating Modes: Constant Frequency,}
Burst Mode^® Operation and PWM
■ _{Available in 32-Pin 5mm × 5mm QFN and}
28-Pin SSOP Packages
U
APPLICATIO S
■ _{Notebook and Palmtop Computers}
■ _{Telecom Systems}
■ _{Portable Instruments}
■ _{Battery-Operated Digital Devices}
■ _{DC Power Distribution Systems}
The LTC^®3728 is a dual high performance step-down
switching regulator controller that drives all N-channel
synchronous power MOSFET stages. A constant fre-
quency 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 microproces-
sor 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.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
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, 6304066, 5705919.
TYPICAL APPLICATIO
M1
L1
3.2µH
+
4.7µF
D3
V_IN PGOOD INTV_CC
TG1
TG2
D4
1µF
C_B1, 0.1µF
f_IN
500kHz
BOOST1
BOOST2
SW1
SW2
LTC3728
BG1
BG2
PLLIN
PGND
C_B2, 0.1µF
V_IN
C_IN
5.2V TO 28V
22µF
M2
50V
L2
3.2µH
R_SENSE1
0.01Ω
V_OUT1
5V
R2
5A
+
105k
C_{OUT1 1%}
47µF
6V
R1
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
R3
20k
1%
1% ^COUT
56µF
6V
SP
M1, M2: FDS6982S
Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter
V_OUT2
3.3V
5A
3728 F01
3728fb
1