LTC3727/LTC3727-1
High Efficiency, 2-Phase
Synchronous Step-Down Switching Regulators
FEATURES
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DESCRIPTIO
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Wide Output Voltage Range: 0.8V
≤
V
OUT
≤
14V
Out-of-Phase Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
OPTI-LOOP
®
Compensation Minimizes C
OUT
±1%
Output Voltage Accuracy
Power Good Output Voltage Monitor
Phase-Lockable Fixed Frequency 250kHz to 550kHz
Latched Short-Circuit Shutdown (LTC3727 Only)
Dual N-Channel MOSFET Synchronous Drive
Wide V
IN
Range: 4V to 36V Operation
Very Low Dropout Operation: 99% Duty Cycle
Adjustable Soft-Start Current Ramping
Foldback Output Current Limiting
Output Overvoltage Protection
Low Shutdown I
Q
: 20µA
Small 28-Lead SSOP Package
LTC3727-1 Also Available in the 5mm
×
5mm QFN
Package
Selectable Constant Frequency or Burst Mode
®
Operation
The LTC
®
3727/LTC3727-1 are high performance dual
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. There is a precision 0.8V reference and a power
good output indicator. A wide 4V to 30V (36V maximum)
input supply range encompasses all battery chemistries.
A RUN/SS pin for each controller provides soft-start, and
on the LTC3727GN, optional timed, short-circuit shut-
down. Current foldback limits MOSFET heat 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 LTC3727/LTC3727-1
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.
APPLICATIO S
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Telecom Systems
Automotive Systems
Battery-Operated Digital Devices
TYPICAL APPLICATIO
8µH
+
4.7µF
M1
0.1µF
M2
TG1
V
IN
PGOOD INTV
CC
TG2
BOOST2
SW2
LTC3727/
LTC3727-1
BG2
PGND
SENSE2
+
1µF
CERAMIC
M3
0.1µF
BOOST1
SW1
BG1
PLLIN
SENSE1
+
0.015Ω
V
OUT1
5V
5A
1000pF
SENSE1
–
V
OSENSE1
105k
1%
I
TH1
20k
1%
220pF
15k
SENSE2
–
1000pF
V
OSENSE2
I
TH2
220pF
15k
20k
1%
280k
1%
+
47µF
6V
SP
M1, M2, M3, M4: FDS6680A
RUN/SS1 SGND RUN/SS2
0.1µF
0.1µF
Figure 1. High Efficiency Dual 12V/5V Step-Down Converter
U
22µF
50V
CERAMIC
V
IN
18V TO 28V
15µH
M4
0.015Ω
V
OUT2
12V
4A
U
U
+
56µF
15V
SP
1628 F01
3727f
1
LINER [ LINEAR TECHNOLOGY ]
