Opto-Electronics


White LED driver integrates audio amplifier

11 July 2007 Opto-Electronics

Maxim has introduced the MAX8678, claiming it to be the industry's only white-LED (WLED) driver to combine a highly efficient negative charge pump with a fully differential, bridged audio amplifier.

Available in a tiny, 3 mm x 3 mm x 0,8 mm TQFN package, this single-chip solution is 50% smaller than the standard two-chip solution.

To achieve high efficiency, the MAX8678 features a negative architecture that completely eliminates high-side in-line resistance, delaying 1x to 2x mode transition during battery discharge. The independent adaptive-mode switching for each LED further extends battery life, even with large LED forward-voltage (Vf) mismatch. These innovative features enable the MAX8678 to be 12% more efficient than competing solutions according to the manufacturer, thus making it ideal for use in cellphones, smartphones, PDAs, and other handheld devices in which space and battery life are precious.

The audio amplifier accepts differential input signals and offers excellent noise immunity to improve audio reproduction. It also delivers 1,1 W to the speaker differentially through a bridge-tied-load (BTL) output stage. This provides up to four times more output power than a conventional, single-ended output stage, thus eliminating the need for output-coupling capacitors and further minimising external component count. The amplifier achieves 90 dB PSRR at 1 kHz and features a flexible, single-wire, serial pulse interface to realise gain settings from -9 dB to +18 dB in 3 dB steps, and it integrates click-and-pop suppression for rich, clean sound quality. It is fully specified for the extended temperature range of -40°C to +85°C.

For more information contact CST Electronics, +27 (0)11 608 0070, ecampling@cstelectronics.co.za, www.cstelectronics.co.za



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