Dual White-LED Driver Ensures Bright Flash In Cell Phone Cameras July 01, 2009
A dual white-LED flash driver maximizes the limited current available in battery-operated digital cameras to increase flash brightness to over 200 lumens and improve picture quality. The ADP1655 inductor-based flash driver improves the reliability of high-resolution camera operation in cell phones, digital still cameras, camcorders, PDAs, and other camera-equipped portable devices, particularly in dark environments. In a cell phone application, the new driver’s proprietary transmit masking function allows the camera flash to run at a higher LED current while simultaneously operating the phone’s RF transceiver to monitor the cellular base station for incoming signals. The ADP1655 integrates a 2-MHz synchronous boost converter, a 500-mA programmable current source, and an I2C interface, which enables timers and currents to be programmed and data to be read back relative to system operation and safety controls. With 5 percent flash-current accuracy, the ADP1655 also improves flash brightness by allowing the camera to increase current to the LED without crossing safety thresholds that would trigger the phone to shut down. The driver also includes a high-side current source that allows the flash LED string to be connected to the camera’s ground plane, eliminating the need to route the LEDs back to the IC. This allows designers to simplify printed-circuit board routing, which reduces circuit trace length and thermal dissipation and allows the camera to be designed using a more compact layout. The ADP1655 is available now in a 12-ball WLSCP with 0.5-mm pitch and a –40°C to +125°C operating temperature range. Pricing is $0.95 in 1000-piece quantities. ANALOG DEVICES INC., Norwood, MA. (781) 328-4700.
Electronic Design China 
