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AMS' LED driver maximises camera flash for smartphones

Posted: 05 Mar 2013 ?? ?Print Version ?Bookmark and Share

Keywords:AMS? LED driver? diagnostic pulse? mobile phone?

Analog IC designer and manufacturer AMS has recently launched a new intelligent LED driver for mobile phone cameras. The AS3649 maximises the brightness of the flash without causing the phone's battery to fall below its minimum operating voltage.

The company's latest LED driver uses an innovative "diagnostic pulse", a burst of controlled high current lasting a few milliseconds, immediately before every flash operation. During this pulse, the device measures the momentary voltage across the terminals of the phone's battery. Based on this measurement, it reports a value for the highest flash drive current the battery can sustain, up to a maximum of 2.5A, avoiding any risk of the phone dropping below its minimum voltage and resetting itself during the main flash.

Mobile phones that use the AS3649 can therefore generate the highest possible level of light for the flash without the need for a bulky auxiliary power source such as a super-capacitor. Users benefit from higher image quality and higher resolution. When taking pictures of fast-moving objects, a brighter flash enables the use of faster shutter speeds for sharper, clearer pictures.

The introduction of the LED driver AS3649 also allows mobile phone manufacturers to reduce the engineering and software development effort involved in flash LED implementation considerably. Today, manufacturers exhaustively test the operation of each mobile phone model's LED flash system under all possible operating conditions, and at a range of operating voltages. The results of these tests are encoded in a software look-up table stored on the phone. Whenever the camera calls for the flash to be operated, the phone's processor must read from the look-up table an estimate for a safe drive current value.

The diagnostic pulse technique made possible by the AS3649 eliminates virtually all of this engineering effort, since it is able to measure the actual behaviour of the battery at the time of use, instead of estimating it beforehand on the basis of sampled test results.

Supplying up to 2.5A to a single LED or up to 1.25A each to two LEDs, the AS3649 is well positioned for next-generation phone cameras using LEDs of higher brightness. The device's current-source architecture provides for effective thermal management, and an on-board NTC (temperature sensor) automatically reduces the current to the LED if it exceeds a programmable temperature threshold.

The AS3649 intelligent flash LED driver is available in volume production now, in 1,000-unit quantities.

Datasheet for the AS3649 can be found here.

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