Charge pump

Analog Devices’ ADM8845 charge pump regulator is designed to deliver accurate backlighting in micro colour TFT LCDs used in cell phones, PDAs and digital cameras.

Analog Devices’ ADM8845 charge pump regulator is designed to deliver accurate backlighting in micro colour thin film transistor (TFT) liquid crystal displays (LCDs) used in cell phones, PDAs and digital cameras.

Using charge pump technology, the device drives up to six white light emitting diodes (LEDs), evenly diffusing light across the entire LCD panel. Precision monitoring of individual LED currents provides matching with less than 1% error.

Its power efficiency of up to 88% helps save battery power while its small lead frame chip scale package (3 mm x 3 mm LFCSP) saves board space.

The ADM8845’s current matching specification has been achieved by individually monitoring the current in each LED, using six individual current control blocks to achieve the 1% maximum matching error, ensuring a uniform backlight across all areas of the LCD panel.

Two control inputs allow the LEDs to be switched on and off in two independent blocks of four LEDs and two LEDs, suiting the device to the latest clam-shell style mobile phones that feature both a main display and a smaller secondary display. The brightness of the LEDs can be adjusted by varying the input signal to these control pins.

To maximize power efficiency, the onboard charge pump automatically switches between 1x, 1.5x and 2x modes, depending on the input voltage from the battery. Soft-start circuitry limits the inrush current to prevent an abrupt start-up.

Manufactured using CMOS process technology, the ADM8845 is available in a 16-lead LFSCP package. Samples are available today and production quantities will be available in July 2004. The ADM8845 is priced at $0.70 per unit in 10,000 piece quantities.

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