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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
IN
Range: 2.7V–7.5V
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 Low Profile Package:
<
1 mm Height -8 Pin LLP
n No External Compensation
Applications
n White LED Display Lighting
n Cellular Phones
n PDAs
Typical Application Circuit
20131601
FIGURE 1. Backlight Configuration
May 2000
LM3557 Step-Up Converter for White LED Applications
© 2006 National Semiconductor Corporation DS201316 www.national.com
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