Boost convertor powers uniform LED backlights

A noninverting boost DC/DC convertor integrated circuit provides a programmable constant-current output of up to 32V from a 2.5-10V DC input for driving white LEDs in series for backlighting.

The new A8431 from Allegro MicroSystems Europe is a noninverting boost DC/DC convertor integrated circuit that provides a programmable constant-current output of up to 32V from a 2.5-10V DC input for driving white LEDs in series for backlighting and other applications in portable battery-operated equipment such as mobile phones, PDAs, MP3 players and cameras.

Up to four white LEDs can be driven at 20mA from a single cell lithium-ion or a multicell NiMH power source, and up to two parallel strings of eight white LEDs can be driven at 20mA by increasing the supply voltage to 10V.

Driving the LEDs in series ensures identical currents and uniform brightness.

The A8431 incorporates a power switch and a feedback sense amplifier to minimise the need for external components.

The output current can be set by adjusting a single external sense resistor, and can be varied with a voltage or a filtered PWM signal when dimming control is required.

The high switching frequency of 1.2MHz allows the use of small inductor and capacitor values.

The device features a 300mA switch current limit and a 1uA shutdown current.

An overvoltage protection pin eliminates the need for an external Zener diode on the output.

The A8431 is provided in a 0.75mm high, 6-pin, 2 x 3mm MLP package.

It is lead-free, with 100% matt tin lead-frame plating.

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