White LED Charge Pump with 1.1W Audio Amplifier

The MAX8678 integrates a charge pump for white light-emitting diodes (LEDs) with an audio loudspeaker amplifier. The high-efficiency, adaptive charge pump drives up to four LEDs with constant current for uniform brightness. The LED current is adjustable from 0.1mA/LED to 24mA/LED in 31 pseudo-logarithmic steps through a single-wire serial-pulse interface. High accuracy and LED-to-LED current matching are maintained throughout the adjustment range. Individual adaptive mode switching for each LED provides high efficiency with a wide range of LED forward voltages.

The mono class AB audio amplifier directly drives an 8Ω loudspeaker with 1.1W RMS continuous power from a 5V supply with less than 1% THD+N. The gain is adjustable from -9dB to +18dB in ten 3dB steps through a single-wire serial-pulse interface. Clicks and pops are suppressed during on/off and all gain adjustments. Differential inputs improve common-mode noise rejection.

The MAX8678 includes soft-start, thermal shutdown, open-circuit and short-circuit protection, and is available in the 16-pin, 3mm x 3mm Thin QFN package (0.8mm max height).

Applications

* Camera Phones * Cell Phones and Smartphones * PDAs, Digital Cameras, Camcorders

* High-Efficiency White LED Charge Pump

* Individual Adaptive Supply for Each LED

* 4 Low-Dropout LED Current Regulators

* 24mA to 0.1mA Dimming Range

* Single-Wire, Serial-Pulse Dimming Interface

* 1% (typ) Accuracy

* Low 140µA Quiescent Current

* Mono Class AB Audio Amplifier

* 1.1W RMS Mono BTL Output (8Ω, VIN = 5V)

* Low 0.004% THD+N at 1kHz

* High 90dB PSRR at 1kHz

* Fully Differential Inputs

* -9dB to +18dB Gain Settings in 3dB Steps

* Integrated Click/Pop Suppression

* Low Quiescent Current

* Soft-Start Limits Inrush Current

* Thermal Shutdown, Open- and Short-Circuit Protection

* 16-Pin, 3mm x 3mm Thin QFN Package