LM3500

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SNVS231F – MAY 2004 – REVISED APRIL 2007

LM3500 Synchronous Step-up DC/DC Converter for White LED Applications

Check for Samples: LM3500

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FEATURES

input and output

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Thermal Shutdown

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Synchronous rectification, high efficiency and

no external schottky diode required

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0.1µA shutdown current

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Uses small surface mount components

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Small 8-bump thin micro SMD package

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Can drive 2-5 white LEDs in series

APPLICATIONS

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LCD Bias Supplies

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2.7V to 7V input range

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White LED Backlighting

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Internal output over-voltage protection (OVP)

circuitry, with no external zener diode required

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Handheld Devices

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LM3500-16: 15.5V OVP; LM3500-21: 20.5V

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Digital Cameras

OVP.

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Portable Applications

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True shutdown isolation

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Input undervoltage lockout

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Requires only small ceramic capacitors at the

DESCRIPTION

The LM3500 is a fixed-frequency step-up DC/DC converter that is ideal for driving white LEDs for display

backlighting and other lighting functions. With fully intergrated synchronous switching (no external schottky diode

required) and a low feedback voltage (500mV), power efficiency of the LM3500 circuit has been optimized for

lighting applications in wireless phones and other portable products (single cell Li-Ion or 3-cell NiMH battery

supplies). The LM3500 operates with a fixed 1MHz switching frequency. When used with ceramic input and

output capacitors, the LM3500 provides a small, low-noise, low-cost solution.

Two LM3500 options are available with different output voltage capabilities. The LM3500-21 has a maximum

output voltage of 21V and is typically suited for driving 4 or 5 white LEDs in series. The LM3500-16 has a

maximum output voltage of 16V and is typically suited for driving 3 or 4 white LEDs in series (maximum number

of series LEDs dependent on LED forward voltage). If the primary white LED network should be disconnected,

the LM3500 uses internal protection circuitry on the output to prevent a destructive over-voltage event.

A single external resistor is used to set the maximum LED current in LED-drive applications. The LED current

can easily be adjusted using a pulse width modulated (PWM) signal on the shutdown pin. In shutdown, the

LM3500 completely disconnects the input from output, creating total isolation and preventing any leakage

currents from trickling into the LEDs.

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PRODUCTION DATA information is current as of publication date.

Copyright © 2004–2007, Texas Instruments Incorporated

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.