Austriamicrosystems has launched the AS3685, a 700mA charge-pump-based flash LED driver. The AS3685 is a charge-pump based flash LED driver offering 700mA flash current and is targeted at camera flash applications in mobile phones. Measuring 2x1.5mm it takes up 14mm2 of PCB space, including four external components. The only external components that the AS3685 needs are capacitors and resistors. Safety in operation is another key requirement for flash LED applications, including low EMI and safe operation under heavy load conditions. Using switched capacitor circuitries to drive large LED currents on the output means pulling high currents from the batteries. The AS3685's smart charge pump architecture avoids large spikes at the battery terminals, providing significantly better EMC performance than comparable products.

To avoid excessive current being drawn from the battery if the phone’s power amplifier becomes active while a picture is being taken – a situation potentially causing the phone to shut down due to a related voltage drop – the AS3685 can reduce the flash current to the significantly lower flash current within less than a microsecond. This prevents dropped calls without compromising photo quality. Other safety features include a built-in flash LED time-out function that guarantees flash shutdown via a built-in factory-programmable timer, typically 800ms. This prevents the destruction of the LED or damage to the mobile phone from excessive heat produced by the LED. The device comes with a multi-mode, 2-pin interface incorporating off, indicator, flashlight and flash operating modes.

The AS3685B product variant features a single-wire interface allowing the flash current to be set in any of 18 different steps depending on actual operating and environmental conditions. This allows to dynamically reduce the flash current during MP3 playback or at low battery conditions. The AS3685 is available in WL-CSP3x4 packaging. It is currently in trials and will be released to mass production in February 2007.