LTC1435
High Efficiency Low Noise
Synchronous Step-Down
Switching Regulator
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DESCRIPTION
FEATURES
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The LTC®1435 is a synchronous step-down switching
regulator controller that drives external N-channel power
MOSFETs using a fixed frequency architecture. Burst
ModeTM operation provides high efficiency at low load
currents. A maximum duty cycle limit of 99% provides low
dropout operation which extends operating time in battery-operated systems.
Dual N-Channel MOSFET Synchronous Drive
Programmable Fixed Frequency
Wide VIN Range: 3.5V to 36V Operation
Ultrahigh Efficiency
Very Low Dropout Operation: 99% Duty Cycle
Low Standby Current
Secondary Feedback Control
Programmable Soft Start
Remote Output Voltage Sense
Logic Controlled Micropower Shutdown: IQ < 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
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 which 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).
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APPLICATIONS
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Notebook and Palmtop Computers, PDAs
Cellular Telephones and Wireless Modems
Portable Instruments
Battery-Operated Devices
DC Power Distribution Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
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TYPICAL APPLICATION
COSC
68pF
VIN
4.5V TO 28V
COSC
RUN/SS
CSS
0.1µF
CC
330pF
VIN
TG
ITH
SW
M1
Si4412DY
BOOST
100pF
VOSENSE
SENSE –
BG
RSENSE
0.033Ω
VOUT
2.9V/3.5A
R1
32.4k
CB
0.1µF
INTVCC
SGND
CIN
22µF
35V
×2
L1
10µH
DB
CMDSH-3
LTC1435
RC
10k
+
+
4.7µF
M2
Si4412DY
R2
22.1k
D1
MBRS140T3
COUT
+ 100µF
10V
×2
PGND
SENSE +
1000pF
1435 F01
Figure 1. High Efficiency Step-Down Converter
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