Sunnyvale, Calif. - Advanced Analogic Technologies Inc.'s AAT3123/4 white-LED drivers are constant-frequency charge pump dc/dc converters that use a dual-mode load switch and fractional (1.5x) conversion to maximize efficiency for white-LED applications.
The parts produce current levels up to 20 milliamps to drive up to six LEDs from a 2.7- to 5.5-volt input. Outputs may be operated individually or paralleled for driving higher-current LEDs. The AAT3123 drives four LEDs while the AAT3124 drives six.
The use of constant-current outputs is said to ensure uniform LED brightness regardless of differences in manufacturing lots. They also eliminate the need for current-limiting resistors. The charge pump design produces significantly lower electromagnetic interference and noise than an inductor-based boost converter, the company said. The white-LED drivers are also said to reduce part count and system footprint. A high (1-MHz) switching frequency enables the use of very small, 1-microfarad external capacitors: two charge pump flying capacitors and one each for Vin and Vout.
The drivers use 32-level, logarithmic-scale LED brightness control through a single-wire digital input using a simple serial-control interface. This approach provides a simpler design than offerings that require a pulse-width modulation signal to control LED brightness, said Erik Ogren, product-marketing manager.
The AAT3123 is packaged in a 12-pin TSOPJW-12 and the AAT3124 in a 16-pin 4 x 4 QFN. Both are pin-compatible with the company's existing AAT3113/4 parts. In lots of 1,000, the AAT3123 sells for $1.80 and the AAT3124 for $2.04.
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