Electronic Design

Charge Pumps Efficiently Drive White LEDs

By employing dual-mode operation, the AAT3123/4 charge-pump white LED drivers achieve high efficiency over the discharge cycle of a lithium-ion battery. The chips combine a 1× load switch with a 1.5× fractional charge pump. During most of the battery's discharge cycle, when the voltage is above the 3.5 V typically needed to drive a white LED, the load switch operates. When the battery voltage goes low, the 1.5× charge pump activates, providing low-noise constant-frequency operation.

The chips have six outputs, each able to drive an LED at up to 20 mA. The AAT3123/4 also boast a unique control scheme. A serial digital input enables, disables, and sets the LED drive current with a 32-level log scale brightness control. The IC also requires only four external components (four 1-µF capacitors). Packaging options include a 16-pin QFN (AAT3124) or a 12-pin TSOP (AAT3123). Pricing in 1000-piece lots starts at $1.80.

See associated figure

Advanced Analogic Technologies
Erik Ogren, (408) 737-4654

TAGS: Components
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