LTC3728LCGN-PBF Datasheet, PDF (1/38 Pages) Linear Technology – Dual, 550kHz, 2-Phase Synchronous Regulators

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 (LTC3728LC)}
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: 4.5V to 28V 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 _{Low Shutdown IQ: 20µA}
n _{5V and 3.3V Standby Regulators}
n _{3 Selectable Operating Modes: Constant-Frequency,}
Burst Mode^® Operation and PWM
n _{5mm × 5mm QFN and 28-Lead Narrow SSOP}
Packages
Applications
n _{Notebook and Palmtop Computers}
n _{Telecom Systems}
n _{Portable Instruments}
n _{Battery-Operated Digital Devices}
n _{DC Power Distribution Systems}
LTC3728L/LTC3728LX
Dual, 550kHz, 2-Phase
Synchronous Regulators
Description
The LTC^®3728L/LTC3728LX are dual high performance
step-down switching regulator controllers that drive 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 microproces-
sor generations, and a wide 4.5V to 28V (30V 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 LTC3728L/LTC3728LX include
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, OPTI-LOOP and PolyPhase
are registered trademarks of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
Typical Application
M1
L1
3.2µH
D1
+
4.7µF
D3
V_IN PGOOD INTV_CC
D4
TG1
TG2
C_B1, 0.1µF
f_IN
500kHz
BOOST1
BOOST2
SW1
SW2
LTC3728L/
BG1 _LTC3728LX BG2
PLLIN
PGND
C_B2, 0.1µF
1µF
CERAMIC
M2
D2
C_IN
22µF
V_IN
5.2V TO 28V
50V
CERAMIC
L2
3.2µH
R_SENSE1
0.01Ω
V_OUT1
5V
5A
R2
105k
+
C_OUT1
47µF
1%
6V
SP
M1, M2: FDS6982S
SENSE1⁺
SENSE2⁺
1000pF
1000pF
SENSE1^–
SENSE2^–
V_OSENSE1
V_OSENSE2
I_TH1
I_TH2
R1
C_C1
220pF
RUN/SS1 SGND RUN/SS2
C_C2
220pF
20k
1%
R_C1
15k
C_SS1
0.1µF
C_SS2
0.1µF
R_C2
15k
R_SENSE2
0.01Ω
R4
63.4k
R3
1%
20k
1%
C_OUT
56µF
6V
SP
V_OUT2
3.3V
5A
3728 F01
Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter
3728lxff
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