FEATURES
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LTC3728L/LTC3728LX
Dual, 550kHz, 2-Phase
Synchronous Regulators
DESCRIPTIO
The LTC
®
3728L/LTC3728LX are dual high performance
step-down switching regulator controllers that drive all
N-channel synchronous power MOSFET stages. A con-
stant 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.
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Dual, 180° Phased Controllers Reduce Required
Input Capacitance and Power Supply Induced Noise
OPTI-LOOP
®
Compensation Minimizes C
OUT
±1%
Output Voltage Accuracy (LTC3728LC)
Power Good Output Voltage Indicator
Phase-Lockable Fixed Frequency 250kHz to 550kHz
Dual N-Channel MOSFET Synchronous Drive
Wide V
IN
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
Low Shutdown I
Q
: 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
APPLICATIO S
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Notebook and Palmtop Computers
Telecom Systems
Portable Instruments
Battery-Operated Digital Devices
DC Power Distribution Systems
TYPICAL APPLICATIO
+
4.7µF
M1
L1
3.2µH
D3
V
IN
PGOOD INTV
CC
TG1
C
B1
, 0.1µF
BOOST1
SW1
BG1
f
IN
500kHz
PLLIN
SENSE1
+
R
SENSE1
0.01Ω
V
OUT1
5V
5A
1000pF
SENSE1
–
V
OSENSE1
C
C1
220pF
R
C1
15k
I
TH1
C
SS1
0.1µF
SENSE2
–
V
OSENSE2
I
TH2
C
SS2
0.1µF
C
C2
220pF
R
C2
15k
LTC3728L/
LTC3728LX
TG2
BOOST2
SW2
BG2
PGND
SENSE2
+
1000pF
C
B2
, 0.1µF
D4
1µF
CERAMIC
M2
+
R2
105k
C
OUT1
1%
47µF
6V
SP
M1, M2: FDS6982S
R1
20k
1%
RUN/SS1 SGND RUN/SS2
Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter
U
U
U
V
IN
5.2V TO 28V
C
IN
22µF
50V
CERAMIC
L2
3.2µH
R
SENSE2
0.01Ω
V
OUT2
3.3V
5A
R3
20k
1%
R4
63.4k
1%
C
OUT
56µF
6V
SP
+
3728 F01
3728lxfa
1
LINER [ LINEAR TECHNOLOGY ]
