LTC1628-PG_15 Datasheet, PDF (1/32 Pages) Linear Technology – High Efficiency, 2-Phase Synchronous Step-Down Switching Regulators

LTC1628/LTC1628-PG
High Efficiency, 2-Phase
Synchronous Step-Down Switching Regulators
FEATURES
s _{Out-of-Phase Controllers Reduce Required Input}
Capacitance and Power Supply Induced Noise
s _OPTI-LOOP^® _{Compensation Minimizes COUT}
s _{±1% Output Voltage Accuracy}
s _{Dual N-Channel MOSFET Synchronous Drive}
s _{Power Good Output Voltage Monitor (LTC1628-PG)}
s _{DC Programmed 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 _{Selectable Constant Frequency or Burst Mode}^®
Operation
s _{Available in 5mm × 5mm QFN and}
28-Pin SSOP Pac_Ukages
APPLICATIO S
s _{Notebook and Palmtop Computers, PDAs}
s _{Battery Chargers}
s _{Portable Instruments}
s _{Battery-Operated Digital Devices}
s _{DC Power Distribution Systems}
DESCRIPTIO
The LTC^®1628/LTC1628-PG 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 adjust-
ment of the frequency 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-PG includes a power
good output pin that replaces the FLTCPL, fault coupling
control pin of the LTC1628.
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP and Burst Mode are registered 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%
M1
M2
R1
20k
1%
+
4.7µF
C_B1, 0.1µF
D3
V_IN
TG1
INTV_CC
TG2
BOOST1
BOOST2
SW1
SW2
LTC1628
BG1
BG2
1000pF
C_C1
220pF
R_C1
15k
SGND
SENSE1⁺
PGND
SENSE2⁺
SENSE1^–
V_OSENSE1
I_TH1
RUN/SS1
C_SS1
0.1µF
SENSE2^–
V_OSENSE2
I_TH2
RUN/SS2
C_SS2
0.1µF
1µF
D4
CERAMIC
M3
C_B2, 0.1µF
M4
1000pF
C_C2
220pF
R3
R_C2
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
1628fb
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