Diodes Charge Pump Simplifies Led Driving in Portable Products

The AL3157 from Diodes Incorporated is a dual function charge pump, capable of handling the competing requirements of LED driving in LCD backlighting and flashlight or camera flash circuits. Provided in the compact 12-pin 3mm x 3mm DFN package and needing the support of only three external capacitors, the device is well suited to portable, battery powered products such as ruggedized mobile phones. Operating from a regular 2.7V to 5.5V supply, this high efficiency charge pump drives 3 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% power efficiency increases battery life and therefore mobile phone talk time, while its 1% current matching accuracy between channels ensures consistency in backlighting resulting in a higher quality screen image. Simple to control, the AL3157 uses only 2 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 solutions, the AL3157 is also more cost effective, being priced at $0.25 each in 1k piece quantities. Further information at http://www.diodes.com