LM3520

Integrated White LED Driver with Organic LED Display

Power Supply

General Description

The LM3520 is a dual step-up DC/DC converter, designed to

drive up to 5 white LEDs with a constant current and to

power an organic LED display with a constant voltage.

A single external resistor is used to set the maximum LED

current. The LED current can be adjusted by applying a

PWM signal to the EN pin. For higher efficiency the LM3520

operates with pulse frequency modulation (PFM) control

scheme when the sub-display is enabled. When Main dis-

play is enabled, the device is operating in PWM mode.

Overvoltage protection circuitry and a 1MHz switching fre-

quency allow for the use of small, low cost external compo-

nents.

Additional features include a low-side NFET switch that can

turn off the LED string with no DC current path to ground.

The LM3520 is available in a small 14-pin thermally-

enchanced LLP package.

Features

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Integrated OLED and white-LED driver

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80% efficiency

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Drives up 5 LEDs at 20mA/3.6V and 4 LEDs at

30mA/3.6V for main-display

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True shutdown isolation

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Small External Components

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1 MHz Switching Frequency

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23V OverVoltage Protection

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Wide Input Voltage Range: 2.7V to 5.5V

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Cycle-By-Cycle Current Limit

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PWM Dimming Control

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Low Profile 14-Pin LLP(3mm x 4mm x 0.8mm)

Applications

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Flip-phones/Clam-shell Cellular Phones

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Handheld Devices

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High-fashion cellular phones

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White LED Backlighting

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Digital Cameras

Typical Applications

20128803

Main Display with OLED Sub Display

PRELIMINARY

February 2005

© 2005 National Semiconductor Corporation

DS201288

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