Intelligent photoflash driver matches LED input with battery output capability in real time



ams, a leading worldwide designer and manufacturer of high-performance analog ICs for consumer & communications, industrial & medical and automotive applications, introduced a new intelligent LED driver for mobile phone cameras that maximizes the brightness of the flash without causing the phone's battery to fall below its minimum operating voltage. The AS3649 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. On the basis of this measurement, it reports a value for the highest flash drive current the battery can sustain, up to a maximum of 2.5A, without dropping below its minimum voltage and triggering the phone to reset itself during the main flash. Drawing on advanced analog sensing technology developed by ams, the AS3649 measures the battery voltage and current with high accuracy, enabling it to precisely calibrate the optimal LED drive current under any given conditions. Mobile phones that use the AS3649 can therefore generate the brightest possible flash light, 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 markedly reduce the engineering and software development effort involved in flash LED implementation. Today, manufacturers exhaustively test the operation of each mobile phone model's LED flash system under all possible operating conditions, and at all 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 implemented by the AS3649 eliminates virtually all of this engineering effort, since it is able to measure the actual behavior 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 higher-brightness LEDs. 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. Ronald Tingl, Senior Marketing Manager at ams, said: "Consumers look carefully at camera performance when choosing a mobile phone - it is a key differentiator. By using the AS3649, handset manufacturers can achieve the best possible lighting for pictures taken in dark conditions, and at the same time benefit from eliminating the huge effort involved in qualifying all components stressed by high LED flash drive currents." The AS3649 intelligent flash LED driver is available in volume production now. It is priced at $0.78 for 1,000 pieces.