LTC1435A
High Efficiency Low Noise
Synchronous Step-Down
Switching Regulator
FEATURES
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DESCRIPTION
The LTC
®
1435A is a synchronous step-down switching
regulator controller that drives external N-channel power
MOSFETs using a fixed frequency architecture. A wide
duty cycle range of 5% to 99% allows high V
IN
to low V
OUT
DC/DC conversion, as well as low dropout operation that
extends operating time in battery-operated systems. Burst
Mode
TM
operation provides high efficiency at low load
currents.
The operating frequency is set by an external capacitor
allowing maximum flexibility in optimizing efficiency. A
secondary winding feedback control pin, SFB, guarantees
regulation regardless of load on the main output by
forcing continuous operation. Burst Mode operation is
inhibited when the SFB pin is pulled low, which reduces
noise and RF interference.
Soft start is provided by an external capacitor that can be
used to properly sequence supplies. The operating cur-
rent 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 is a trademark of Linear Technology Corporation.
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Dual N-Channel MOSFET Synchronous Drive
Programmable Fixed Frequency
Wide V
IN
Range: 3.5V to 36V Operation
Low Minimum On-Time (
≤
300ns) for High
Frequency, Low Duty Cycle Applications
Very Low Dropout Operation: 99% Duty Cycle
Low Standby Current
Secondary Feedback Control
Programmable Soft Start
Remote Output Voltage Sense
Logic Controlled Micropower Shutdown: I
Q
< 25µA
Foldback Current Limiting (Optional)
Current Mode Operation for Excellent Line and Load
Transient Response
Output Voltages from 1.19V to 9V
Available in 16-Lead Narrow SO and SSOP Packages
APPLICATIONS
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Notebook and Palmtop Computers, PDAs
Cellular Telephones and Wireless Modems
Portable Instruments
Battery-Operated Devices
DC Power Distribution Systems
TYPICAL APPLICATION
V
IN
4.5V TO 22V
C
OSC
43pF
C
OSC
C
SS
0.1µF
C
C
330pF
R
C
10k
SGND
100pF
V
OSENSE
SENSE
–
BG
PGND
SENSE
+
RUN/SS
I
TH
LTC1435A
INTV
CC
BOOST
V
IN
TG
SW
M1
Si4412DY
+
C
IN
22µF
35V
×
2
R
SENSE
0.033Ω
D
B
CMDSH-3
C
B
0.1µF
L1
4.7µH
+
4.7µF
M2
Si4412DY
D1
MBRS140T3
1000pF
Figure 1. High Efficiency Step-Down Converter
U
U
U
V
OUT
1.6V/3A
R1
35.7k
R2
102k
+
C
OUT
100µF
6.3V
×
2
1435A F01
1
LINER [ LINEAR TECHNOLOGY ]
