Driver chip pulses 8A to maximise light output for LED photo-flash

July 04, 2013 // By Paul Buckley
ams has launched an LED flash driver that provides a photo flash light output claimed to be at least four times brighter than flash systems commonly found in smartphones today.

The new AS3630 can drive up to 8A current through an LED flash system, enabling mobile smartphone cameras to take sharp images in difficult conditions such as of moving objects in dark conditions, that previously would have suffered from motion artifacts . At the same time, glare and discomfort can be avoided because even short flash durations as low as 10 msec provide sufficient light.
Compared to today’s LED flash drivers in mobile phones typically providing a maximum 2-A output, the AS3630 is rated for an output four times higher and supports substantially faster shutter speeds.
The AS3630 8-A LED flash driver uses an architecture that fully exploits the energy stored inside a supercap (Electric Double Layer Capacitor, or EDLC). Driving two LEDs in series, the output of the supercap is always boosted from 5.5-V to typically higher than 9V, to match the forward voltage of the LEDs. The boost topology employed also keeps the flash illuminated longer when the output from the unassisted capacitor would fall below the LEDs’ forward voltage. This architecture enables the use of the smallest capacitors.
The AS3630 photo flash driver also combines power from the EDLC with power from the phone battery, increasing the power available to the flash light system and supporting additional functions such as pre-flash and video light even when the supercap is discharged.
Driving two flash LEDs in series also provides for consistent light output. Especially in such high power flash applications, parallel LED architectures suffer from high variations in light output from one unit to another because of production variations between LEDs.
The serial LED architecture used by ams solves this problem, delivering a perfectly matched light output from both flash LEDs that is unaffected by variations between LED production units.
To optimise system performance, ams has collaborated with passive component manufacturer Murata, matching the feature set of the AS3630 with thin, high-capacity EDLCs from Murata .
The AS3630