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LTC1435

High Efficiency Low Noise

Synchronous Step-Down

Switching Regulator

Figure 1. High Efficiency Step-Down Converter

FEATURES

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Dual N-Channel MOSFET Synchronous Drive

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Programmable Fixed Frequency

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Ultrahigh Efficiency

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Very Low Dropout Operation: 99% Duty Cycle

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Low Standby Current

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Secondary Feedback Control

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Programmable Soft Start

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Remote Output Voltage Sense

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Foldback Current Limiting (Optional)

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Current Mode Operation for Excellent Line and Load

Transient Response

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Output Voltages from 1.19V to 9V

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Available in 16-Lead Narrow SO and SSOP Packages

The LTC

regulator controller that drives external N-channel power

MOSFETs using a fixed frequency architecture. Burst

Mode

currents. A maximum duty cycle limit of 99% provides low

dropout operation which extends operating time in bat-

tery-operated systems.

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).

, LTC and LT are registered trademarks of Linear Technology Corporation.

Burst Mode is a trademark of Linear Technology Corporation.

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Notebook and Palmtop Computers, PDAs

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Cellular Telephones and Wireless Modems

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Portable Instruments

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Battery-Operated Devices

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DC Power Distribution Systems

TG

68pF

330pF

100pF

10k

0.1

µF

LTC1435

1000pF

+

4.7

µF

CMDSH-3

0.1

µF

M2

Si4412DY

D1

MBRS140T3

L1

10

µH

M1

Si4412DY

0.033

Ω

+

22

µF

35V

× 2

4.5V TO 28V

+

100

µF

10V

× 2

R1

32.4k

R2

22.1k

2.9V/3.5A

PGND

BG

BOOST

1435 F01

SGND

RUN/SS

SW