1
LTC1735
1735fc
High Efficiency
Synchronous Step-Down
Switching Regulator
The LTC
®
1735 is a synchronous step-down switching
regulator controller that drives external N-channel power
MOSFETs using a fixed frequency architecture. Burst
Mode
TM
operation provides high efficiency at low load
currents. The precision 0.8V reference is compatible with
future generation microprocessors. OPTI-LOOP compen-
sation allows the transient response to be optimized over
a wide range of output capacitance and ESR values.
The operating frequency (synchronizable up to 500kHz) is
set by an external capacitor allowing maximum flexibility
in optimizing efficiency. A forced continuous control pin
reduces noise and RF interference and can assist second-
ary winding regulation by disabling Burst Mode operation
when the main output is lightly loaded.
Protection features include internal foldback current lim-
iting, output overvoltage crowbar and optional short-
circuit shutdown. Soft-start is provided by an external
capacitor that can be used to properly sequence supplies.
The operating current level is user-programmable via an
external current sense resistor. Wide input supply range
allows operation from 4V to 30V (36V maximum).
■
Synchronizable/Programmable Fixed Frequency
■
OPTI-LOOP
TM
Compensation Minimizes C
OUT
■
±
1% Output Voltage Accuracy
■
Dual N-Channel MOSFET Synchronous Drive
■
Wide V
IN
Range: 4V to 36V Operation
■
V
OUT
Range: 0.8V to 6V
■
Internal Current Foldback
■
Output Overvoltage Crowbar Protection
■
Latched Short-Circuit Shutdown Timer
with Defeat Option
■
Very Low Dropout Operation: 99% Duty Cycle
■
Forced Continuous Control Pin
■
Optional Programmable Soft-Start
■
Remote Output Voltage Sense
■
Power Good Output (LTC1735F Only)
■
Logic Controlled Micropower Shutdown: I
Q
< 25µA
■
LTC1435 Pin Compatible with
Minor Component Changes
■
Available in 16-Lead Narrow SSOP, SO Packages and
20-Lead TSSOP Package (LTC1735F Only)
Figure 1. High Efficiency Step-Down Converter
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation.
■
Notebook and Palmtop Computers, PDAs
■
Cellular Telephones and Wireless Modems
■
DC Power Distribution Systems
C
OSC
RUN/SS
TG
BOOST
LTC1735
C
B
0.22µF
100pF
C
C
330pF
R
C
33k
R
SENSE
0.005Ω
V
OUT
1.6V
9A
C
OUT
: PANASONIC EEFUEOG181R
C
IN
: MARCON THCR70E1H226ZT
L1: PANASONIC ETQP6F2R0HFA
R
SENSE
: IRC LRF2010-01-R005J
1000pF
C
SS
0.1µF
C
OSC
47pF
+
4.7µF
+
C
OUT
180µF
4V
×4
SP
C
IN
22µF
50V
M1
FDS6680A
M2
FDS6680A
1735 F01
D
B
CMDSH-3
D1
MBRS340T3
V
IN
5V TO 24V
L1
2µH
C
C2
100pF
R2
20k
1%
R1
20k
1%
SGND
V
OSENSE
SENSE
–
SENSE
+
INTV
CC
BG
PGND
I
TH
SW
V
IN
FEATURES
DESCRIPTIO
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APPLICATIO S
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TYPICAL APPLICATIO
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