Electronic Design

High-Efficiency Class D Audio Amp Goes Filter-Free

The originator of the "best-in-class" Boomer audio technology, National Semiconductor Corp., has unveiled a filterless, high-efficiency Class D Boomer audio amplifier. It comes in a tiny micro nine-bump surface-mount device (SMD) package that suits cellular phones and portable consumer devices. Maximum package dimensions, including the bumps, are 1.514 mm wide by 1.514 mm long by 0.600 mm high.

The fixed-gain LM4667 features typical efficiency levels of 86%, 84%, and 74% at 5 V, 3 V, and 3 V, respectively, when driving an 8-Ω transducer. It has a total quiescent current of 3.5 mA and shutdown current of just 0.01 µA for a supply voltage range of 2.7 to 5.5 V.

"Eliminating the output filter for inductive transducers reduces the number of parts and board area needed, which simplifies the circuit design for our customers," says Gary Adrig, National's marketing director for the Audio Products Group. "Since many of our customers now use cellular phones as their primary phones, talk times are increasing, which creates the need for longer battery life. The LM4667 fulfills this need by delivering high efficiency, lower operating temperatures, and longer battery life."

The LM4667 features an innovative modulator that eliminates the need for an output filter. It processes analog inputs with a delta-sigma modulator that lowers output noise and total harmonic distortion plus noise (THD+N) of less than 1% with a continuous average output of 450 mW. The device offers fixed selectable gains of either 6 or 12 dB, a 5-ms turn-on time, and short-circuit protection. It operates from −40°C to 85°C.

Available now, the LM4667 goes for $0.48 each in 1000-unit quantities.

National Semiconductor Corp.
(800) 272-9959

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