LTC3728L/LTC3728LX
1
3728lxff
Typical applicaTion
FeaTures
applicaTions
DescripTion
Dual, 550kHz, 2-Phase
Synchronous Regulators
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.
Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter
n
Dual, 180° Phased Controllers Reduce Required
Input Capacitance and Power Supply Induced Noise
n
OPTI-LOOP
®
Compensation Minimizes C
OUT
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 V
IN
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 I
Q
: 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
n
Notebook and Palmtop Computers
n
Telecom Systems
n
Portable Instruments
n
Battery-Operated Digital Devices
n
DC Power Distribution Systems
+
4.7µF
D3
D4
M1
C
B1
, 0.1µF
R2
105k
1%
1000pF
D1
L1
3.2µH
C
C1
220pF
1µF
CERAMIC
C
IN
22µF
50V
CERAMIC
+
C
OUT1
47µF
6V
SP
R
SENSE1
0.01Ω
R1
20k
1%
R
C1
15k
V
OUT1
5V
5A
M2
D2
C
B2
, 0.1µF
R4
63.4k
1%
L2
3.2µH
C
C2
220pF
1000pF
+
C
OUT
56µF
6V
SP
R
SENSE2
0.01Ω
R3
20k
1%
R
C2
15k
V
OUT2
3.3V
5A
TG1 TG2
BOOST1 BOOST2
SW1 SW2
BG1 BG2
SGND
PGND
SENSE1
+
SENSE2
+
SENSE1
–
SENSE2
–
V
OSENSE1
V
OSENSE2
I
TH1
I
TH2
V
IN
PGOOD INTV
CC
RUN/SS1 RUN/SS2
V
IN
5.2V TO 28V
M1, M2: FDS6982S
3728 F01
C
SS1
0.1µF
C
SS2
0.1µF
LTC3728L/
LTC3728LX
PLLIN
f
IN
500kHz
