Supercapacitor powers LED flash
By Paul Rako, Technical Editor -- EDN, May 27, 2008
has introduced a 2-MHz boost-converter IC that uses a supercapacitor to provide a large peak current to an LED-flash system. The 2A AAT1282 flash driver incorporates I2C control and accepts input voltages of 2.7 to 5.5V. Designers can use the device’s two 1A current sinks to drive two LEDs and can parallel these outputs to drive one 2A LED. The IC allows designers to set 16 levels for movie, or “torch,” mode and has a true-load-disconnection feature that guarantees a shutdown current of less than 1 μA. The device achieves 90% efficiency with a 1-μH inductor.
Using a supercapacitor to provide for a reservoir of current, the product protects the batt
ery from high-discharge events and allows LED brightness approaching that of a xenon flash. The 0.55F supercapacitor comprises two 2.5V capacitors so that the IC can always operate in boost mode. The circuit also includes 2.2-μF ceramic capacitors to reduce ac-circulating currents, yielding lower EMI (electromagnetic-interference) emissions and ensuring that current from the supercapacitor doesn’t flow back into the battery.
The AAT1282 is available in a 14-pin, 3×3-mm, TDFN (thin-dual-inline-flat) package with a suggested retail price of $1.75 (1000). The IC operates across a −40 to +85°C temperature range. Samples and evaluation modules are available now.
