Charge Pump Suits Portable Battery-Powered Devices

The AL3157 from Diodes Incorporated is a dual-function charge pump, capable of handling the competing requirements of LED driving in LCD backlighting, as well as flashlight or camera-flash circuits. Provided in a compact 12-pin, 3 x 3mm DFN package and requiring the support of only three external capacitors, the device is suitable for portable, battery-powered products such as ruggedised mobile phones.

Operating from a regular 2.7-5.5V supply, this charge pump drives three channels at up to 30mA for small LCD-screen backlighting and a separate channel at up to 210mA for LED flashlight or LED camera flash. Its 93 per cent power efficiency increases battery life and therefore mobile-phone talk time, while its one per cent current matching accuracy between channels ensures consistency in backlighting, resulting in a higher-quality screen image.

Simple to control, the AL3157 uses only two enable pins to enable and disable the associated LCD backlighting and camera-flash output channels and to dim the LED current delivered using pulse width modulation. To maximise reliability, all output channels incorporate short-circuit, thermal and under-voltage lockout protection. More compact and less complicated than alternative charge-pump devices, the AL3157 is also more cost effective, being priced at USD0.25 (GBP0.16) each in 1,000-piece quantities.

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