LM3557

Step-Up Converter for White LED Applications

General Description

The LM3557 is a complete solution for white LED drive

applications. With minimal external component count, no DC

current leakage paths to ground, cycle-by-cycle current limit

protection, and output over-voltage protection circuitry, the

LM3557 offer superior performance and cost savings over

standard DC/DC boost component implementations.

The LM3557 switches at a fixed-frequency of 1.25 MHz,

which allows for the use of small external components. Also,

the LM3557 has a wide input voltage range to take advan-

tage of multi-cell input applications. With small external com-

ponents, high fixed frequency operation, and wide input

voltage range, the LM3557 is the most optimal choice for

LED lighting applications.

Features

n

V

n

Small External Components

n

1.25 MHz Constant-Switching Frequency

n

Output Over-Voltage Protection

n

Input Under-Voltage Protection

n

Cycle-By-Cycle Current Limit

n

TRUE SHUTDOWN: No DC current paths to ground

during shutdown

n

n

No External Compensation

Applications

n

White LED Display Lighting

n

Cellular Phones

n

PDAs

Typical Application Circuit

20131601

FIGURE 1. Backlight Configuration

November 2004

© 2004 National Semiconductor Corporation

DS201316

www.national.com