Power Electronics

Smart 1-A Charge Pump for Flash LEDs

Austriamicrosystems AG, a designer and manufacturer of analog integrated circuits (ICs), has unveiled a smart 1-A charge pump for flash LEDs in camera phones. Extending the company's lighting IC portfolio, the two high-current charge pumps, the AS3682 and the AS3683, drive flash LEDs with up to 480-mA and 1-A output current, respectively.

The ICs achieve a peak efficiency of 95% (PLed/Pin) due to supporting automatic mode switching between 1x/1.5x and 2x modes and through their ultralow dropout current sinks. The six current sinks can be used with individual LEDs connected in parallel or tied together for driving a single high-output LED.

The output currents can be adjusted between 15 mA and 1 A by either a serial interface using soft flash mode or a simple parallel interface using hard flash mode. The hard flash mode is implemented as a 3-pin enable/disable function so that eight different currents can be set for both preview and flash by using only two control wires.

This hard flash control method significantly reduces the software effort to embed the IC into a handheld device. The preview and flash start times and duration are controlled individually by either the interfaces or via dedicated preview and strobe inputs. The strobe duration can be set in 100 ms steps up to a maximum of 800 ms. Usig the dedicated preview and strobe pins enables virtually indefinite lighting duration for easy realization of movie light and lamp functions.

Three out of six LEDs can be addressed independently so that additional functions like a movie indicator lamp, a RGB Fun LED or Backlighting can be realized with a minimum of additional components.

The charge pump runs at a fixed frequency of 1 MHz requiring only two transfer capacitors. In addition, the AS3682 features two programmable general purpose I/Os (GPIOs), a soft-start function to limit inrush currents, overvoltage protection, thermal shutdown and zero LED current during shutdown. The AS3682 is available in a space-saving 4-mm × 4-mm QFN24 package.

For more information, visit www.austriamicrosystems.com.

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