LTC1628-SYNC Datasheet, PDF (1/32 Pages) Linear Technology – High Efficiency, 2-Phase Synchronous Step-Down Switching Regulator

LTC1628-SYNC
High Efficiency, 2-Phase
Synchronous Step-Down Switching Regulator
FEATURES
s _{Out-of-Phase Controllers Reduce Required Input}
Capacitance and Power Supply Induced Noise
s _OPTI-LOOP^TM _{Compensation Minimizes COUT}
s _{Dual N-Channel MOSFET Synchronous Drive}
s _{±1% Output Voltage Accuracy}
s _{Power Good Output Voltage Monitor}
s _{Phase-Lockable Fixed Frequency 150kHz to 300kHz}
s _{Wide VIN Range: 3.5V to 36V Operation}
s _{Very Low Dropout Operation: 99% Duty Cycle}
s _{Adjustable Soft-Start Current Ramping}
s _{Foldback Output Current Limiting}
s _{Latched Short-Circuit Shutdown with Defeat Option}
s _{Output Overvoltage Protection}
s _{Remote Output Voltage Sense}
s _{Low Shutdown IQ: 20µA}
s _{5V and 3.3V Standby Regulators}
s _{Small 28-Lead SSOP Package}
s _{Selectable Constant Frequency or Burst Mode}^TM
Operation
U
APPLICATIO S
s _{Notebook and Palmtop Computers, PDAs}
s _{Telecom Systems}
s _{Portable Instruments}
s _{Battery-Operated Digital Devices}
s _{DC Power Distribution Systems}
DESCRIPTIO
The LTC^®1628-SYNC is a high performance dual step-
down switching regulator controller that drives all
N-channel synchronous power MOSFET stages. A con-
stant frequency current mode architecture allows phase-
lockable frequency of up to 300kHz. 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 3.5V to 30V (36V 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 LTC1628-SYNC includes 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 trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
L1
6.3µH
D1
V_OUT1
5V
5A
R_SENSE1
0.01Ω
+
C_OUT1
47µF
6V
SP
R2
105k
1%
+
4.7µF
M1
C_B1, 0.1µF
M2
D3
V_IN PGOOD INTV_CC
TG1
TG2
BOOST1
BOOST2
SW1
SW2
LTC1628-SYNC
BG1
BG2
1µF
D4
CERAMIC
M3
C_B2, 0.1µF
M4
f_IN
1000pF
PLLIN
SENSE1⁺
SENSE1^–
PGND
SENSE2⁺
SENSE2^–
1000pF
V_OSENSE1
V_OSENSE2
I_TH1
I_TH2
R1
C_C1
220pF
RUN/SS1 SGND RUN/SS2
C_C2
220pF
R3
20k
1%
R_C1
15k
C_SS1
0.1µF
C_SS2
R_C2
0.1µF
15k
20k
1%
V_IN
C_IN ^{5.2V TO 28V}
22µF
50V
CERAMIC
L2
6.3µH
D2
R_SENSE2
0.01Ω
R4
63.4k
1%
C_OUT
56µF
6V
SP
V_OUT2
3.3V
5A
M1, M2, M3, M4: FDS6680A
1628 F01
Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter
1