LED flash driver improves picture quality in mobile phones

The AS3645 LED flash driver from austriamicrosystems is an inductive, ultra small, high-efficiency single/dual LED flash driver that offers 25% higher output current than existing equivalents. The higher flash power enhances picture and video quality especially in low-light environments at the same system size.

The AS3645 inductive flash driver drives up to 1000 mA and can be used in single LED flash or double LED flash environments. The high-side current source works with up to 2 x 500 mA with 2 LEDs in serial configuration, and up to 720 mA with 1 LED. When driving 2 LEDs in series, LEDs draw identical currents and provide output light matching and thermal dissipation. The AS3645 auto detects whether to employ single or dual LED mode, and enables direct one-button torch (flashlight) mode.

A number of safety features protect against circuit damage and improve test time, including programmable current limiting, auto test (LED open/short detection), overvoltage and undervoltage, overtemperature, and automatic flash timeout timer for thermal LED protection during flash.

These features suit the needs of a camera phone flash, especially in smart phones and feature-phones. For other devices with cameras, including digital still cameras, camcorders and PDAs, the AS3645 flashlight driver is a suitable solution. Its high-efficiency 2 MHz fixed frequency dc-dc boost converter with soft start allows small coils (inductors) to be used and enables easy integration into noise sensitive RF systems. The high-power LED flash current source can operate in flash, torch, and assist (video) light mode.

An additional current source drives an optional indicator LED. Control can be implemented through either the parallel interface mode to allow simple integration, or the I2C interface to allow more sophisticated control of all settings like currents and timings. The interface is selected by a dedicated pin (I2C/EN). The AS3645 is available in a tiny WL-CSP package (3 x 4 balls 0.5 mm pitch, 2 x 1.6 mm) and has an operating temperature range of -30° to 85° C (ambient).

For more information, contact austriamicrosystems USA Inc., 5201 Great America Parkway, Suite 320, Santa Clara, CA 95054. Phone: 408-345-1790.