LTC3728L/LTC3728LX
Dual, 550kHz, 2-Phase
Synchronous Regulators
FeaTures
DescripTion
Dual, 180° Phased Controllers Reduce Required
The LTC®3728L/LTC3728LX are dual high performance
step-down switching regulator controllers that drive all
N-channelsynchronouspowerMOSFETstages.Aconstant-
frequency,currentmodearchitectureallowsphase-lockable
frequency of up to 550kHz. Power loss and noise due to
theESRoftheinputcapacitorsareminimizedbyoperating
the two controller output stages out of phase.
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Input Capacitance and Power Supply Induced Noise
OPTI-LOOP® Compensation Minimizes C
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OUT
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1ꢀ Output Voltage Accuracy (LTC3728LC)
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Power Good Output Voltage Indicator
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Phase-Lockable Fixed Frequency 250kHz to 550kHz
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Dual N-Channel MOSFET Synchronous Drive
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Wide V Range: 4.5V to 28V Operation
IN
OPTI-LOOPcompensationallowsthetransientresponseto
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.
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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
Low Shutdown I : 20µA
5V and 3.3V Standby Regulators
3 Selectable Operating Modes: Constant-Frequency,
Burst Mode® Operation and PWM
5mm × 5mm QFN and 28-Lead Narrow SSOP
Packages
Q
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
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MOSFET until V
returns to normal. The FCB mode
OUT
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.
applicaTions
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Notebook and Palmtop Computers
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Telecom Systems
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Portable Instruments
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Battery-Operated Digital Devices
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.
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DC Power Distribution Systems
Typical applicaTion
V
IN
5.2V TO 28V
C
22µF
50V
IN
1µF
CERAMIC
+
4.7µF
D3
D4
V
PGOOD INTV
IN
CC
CERAMIC
M1
M2
TG1
TG2
L1
3.2µH
L2
3.2µH
BOOST1
SW1
BOOST2
SW2
C
, 0.1µF
C
B2
, 0.1µF
B1
LTC3728L/
LTC3728LX
BG1
BG2
D1
D2
f
IN
500kHz
PLLIN
PGND
+
+
SENSE1
SENSE2
R
R
SENSE2
0.01Ω
SENSE1
1000pF
1000pF
0.01Ω
–
–
SENSE1
V
SENSE2
V
V
3.3V
5A
OSENSE1
TH1
OSENSE2
V
OUT2
OUT1
5V
5A
R2
105k
1%
R4
63.4k
1%
I
I
TH2
C
C
C2
C1
220pF
C
47µF
6V
C
56µF
6V
RUN/SS1 SGND RUN/SS2
OUT1
OUT
220pF
R
C2
+
+
R1
20k
1%
R3
20k
1%
R
C1
C
C
SS2
0.1µF
SS1
0.1µF
15k
15k
SP
SP
M1, M2: FDS6982S
3728 F01
Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter
3728lxff
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