The additional addressing capability of these two buses offers designers tremendous flexibility to modify drive current, and therefore WLED brightness. At the same time, the boost converters' high drive current and small 3x3mm footprint delivers a highly attractive alternative to bulky xenon lamp solutions.
Many digital still cameras and phone cameras today maximize photo quality by compensating for ambient light deviations. By taking advantage of the additional control capabilities in the AS2Cwire and I2C bus, the AAT1271 and AAT1272 allow designers to modify flash brightness or movie mode brightness on-the-fly across multiple levels and thereby improve picture quality.
Both the AAT1271 and AAT1272 are high efficiency, high current boost converters designed for LED photo flash applications. Operating off a 2.7V to 5.5V input voltage range, the two new devices are targeted at single-cell Lithium-ion battery powered mobile systems. Both converters use a high 2MHz switching frequency which helps reduce system footprint by allowing the use of smaller external inductors and capacitors. The two new converters can achieve up to 85% efficiency with 1microH inductors.
The AAT1271 and AAT1272 feature two channels capable of driving two high current WLEDs at up to 750mA each. Alternately, the two channels can be combined to drive a single WLED at up to 1.5A. The AAT1271 features AnalogicTech’s proprietary single-wire AS2C interface, while the AAT1272 offers the industry-standard two-wire I2C interface.
Both converters supply separate flash enable and movie-mode enable inputs to control flash and movie-mode operation. Designers use a single, external resistor to set full-scale flash LED current. A default 7.3:1 flash-to-movie-mode current ratio is provided.
Designers can adjust the movie-mode current level from the default setting to any of 15 other levels using either the AS2Cwire or I2C interface. The AAT1271 also adds a flash inhibit input that can be used in GSM mobile applications to reduce the flash current during PA transmission to avoid a system reset due to excessive battery droop in high battery current conditions.
Given their high drive current capability, both converters also feature input current limit capability and a true load disconnect switch that reduces supply current in shutdown to < 1microA.
The new converters also include a user-programmable flash safety timer. This function can be used to protect the flash LEDs from thermal damage in the event of a software failure by terminating the flash pulse regardless of the FL enable signal condition. Using the AS2C or I2C bus, the safety timer can be programmed across 16 different levels.
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