LM3478

High Efficiency Low-Side N-Channel Controller for

Switching Regulator

General Description

The LM3478 is a versatile Low-Side N-FET switching regu-

lator controller. It is suitable for use in topologies requiring

low side FET, such as boost, flyback, SEPIC, etc. Moreover,

the LM3478 can be operated at extremely high switching

frequency in order to reduce the overall solution size. The

switching frequency of LM3478 can be adjusted to any value

between 100kHz and 1MHz by using a single external resis-

tor. Current mode control provides superior bandwidth and

transient response, besides cycle-by-cycle current limiting.

Output current can be programmed with a single external

resistor.

The LM3478 has built in features such as thermal shutdown,

short-circuit protection, over voltage protection, etc. Power

saving shutdown mode reduces the total supply current to

5µA and allows power supply sequencing. Internal soft-start

limits the inrush current at start-up.

Key Specifications

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Wide supply voltage range of 2.97V to 40V

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100kHz to 1MHz Adjustable clock frequency

2.5% (over temperature) internal reference

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10µA shutdown current (over temperature)

Features

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8-lead Mini-SO8 (MSOP-8) package

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Internal push-pull driver with 1A peak current capability

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Current limit and thermal shutdown

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Frequency compensation optimized with a capacitor and

a resistor

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Internal softstart

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Current Mode Operation

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Undervoltage Lockout with hysteresis

Applications

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Distributed Power Systems

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Battery Chargers

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Offline Power Supplies

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Telecom Power Supplies

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Automotive Power Systems

Typical Application Circuit

10135501

Typical High Efficiency Step-Up (Boost) Converter

May 2003

© 2003 National Semiconductor Corporation

DS101355

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