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WLED driver integrates audio amp, LDOs

Posted: 12 Mar 2008 ?? ?Print Version ?Bookmark and Share

Keywords:WLED driver? audio amplifiers? LDO?

Maxim Integrated Products has introduced the MAX8821, said to be the only white-LED (WLED) driver to combine a highly efficient, negative charge pump with a fully differential, bridged audio amplifier and two low-noise, low-dropout (LDO) current regulators.

To maximize efficiency, this LED driver features a negative architecture that completely eliminates high-side, in-line switch resistance loss in 1x mode, delaying 1x to 1.5x mode transitions during battery discharge.

The MAX8821 uses independent adaptive-mode switching for each LED to further extend battery life, even with large LED forward-voltage (VF) mismatching. Moreover, the audio amplifier accepts differential input signals, offering excellent noise immunity to improve audio reproduction. This performance and integration make the MAX8821 suitable for use in cellphones, smart phones, PDAs and portable media players in which every milliamp-hour of battery life is precious and PCB space is limited.

This innovative device drives six WLEDs with 1 percent accurate current matching. To maximize flexibility, the MAX8821 supports I?C dimming control with 32 pseudo-logarithmic dimming levels. Additionally, this WLED driver achieves low, 70?A quiescent current and features an on-chip, TA derating function that reduces the current above 40C to prevent the LEDs from burning out. The integrated, dual LDO regulators deliver over 200mA of current output with 45?V noise and 60dB PSRR for sensitive circuitry.

The MAX8821's Class D audio amplifier delivers 2W to the speaker differentially by the use of a bridge-tied load (BTL) output stage. This provides up to four times more output power than a conventional, single-ended output stage and eliminates the need for an output-coupling capacitor. In addition, at 1kHz, this device achieves a high, 65dB PSRR gain, which the flexible -3dB to +24dB gain settings realize in 3dB steps. Integrated click-and-pop suppression circuitry ensures rich, clean sound quality.

The MAX8821 is available in a 4mm x 4mm x 0.8mm, 28-pin TQFN package and is fully specified over the -40C to 85C extended temperature range. Prices start at $2.55 (1,000-up, FOB USA).

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