FEATURES
s
s
s
s
s
s
s
s
s
LTC1735
High Efficiency
Synchronous Step-Down
Switching Regulator
DESCRIPTIO
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 microprocessor generations. 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 3.5V to 30V (36V maximum).
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation.
s
s
s
s
s
s
s
Dual N-Channel MOSFET Synchronous Drive
Synchronizable/Programmable Fixed Frequency
Wide V
IN
Range: 3.5V to 36V Operation
V
OUT
Range: 0.8V to 6V
OPTI-LOOP
TM
Compensation Minimizes C
OUT
±
1% Output Voltage Accuracy
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
Logic Controlled Micropower Shutdown: I
Q
< 25µA
LTC1435 Pin Compatible with
Minor Component Changes
Available in 16-Lead Narrow SSOP and SO Packages
APPLICATIO S
s
s
s
Notebook and Palmtop Computers, PDAs
Cellular Telephones and Wireless Modems
DC Power Distribution Systems
TYPICAL APPLICATIO
C
OSC
47pF
C
SS
0.1µF
C
C
330pF
R
C
33k
C
OSC
TG
RUN/SS
BOOST
I
TH
SW
C
C2
100pF
SGND
100pF
V
OSENSE
BG
SENSE
–
1000pF
SENSE
+
PGND
INTV
CC
LTC1735
V
IN
D
B
CMDSH-3
L1
2µH
C
B
0.22µF
M1
FDS6680A
C
IN
22µF
50V
V
IN
5V TO 24V
C
OUT
: PANASONIC EEFUEOG181R
C
IN
: MARCON THCR70E1H226ZT
L1: PANASONIC ETQP6FZR0HFA
R
SENSE
: IRC LRF2010-01-R005J
R
SENSE
0.005Ω
+
4.7µF
M2
FDS6680A
D1
MBRS340T3
Figure 1. High Efficiency Step-Down Converter
U
U
U
V
OUT
1.6V
9A
R1
20k
1%
R2
20k
1%
+
C
OUT
180µF
4V
×
4
SP
1735 F01
1
LINER [ LINEAR TECHNOLOGY ]
