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Filter-less high efficiency Class D audio amplifier sounds right for portable applications

Santa Clara, CA — January 26, 2004 — National Semiconductor Corporation today introduced a filter-less high efficiency Boomer audio amplifier for cellular phones and portable consumer devices.

National's LM4667 is ideal for portable consumer applications such as cellular handsets because of its high efficiency, resulting in less system heat and longer battery life. It is housed in a tiny micro SMD package. The LM4667's fixed gain reduces pin count and eliminates the need for an output filter when it is located near the speaker, resulting in both space and cost savings.

“Eliminating the output filter reduces the number of parts and board area, which simplifies the circuit design for our customers,” said Gary Adrig, marketing director for National Semiconductor's audio products group. “Since many consumers now use cellular phones as their primary phones, talk times are increasing, which creates the need for longer battery life. National's LM4667 fulfills this need by delivering high efficiency, lower operating temperature, and longer battery life.”

National's LM4667 is a fully integrated single-supply, high efficiency switching audio amplifier. It features an innovative modulator that eliminates the output filter used with typical switching amplifiers. The LM4667 processes analog inputs with a delta-sigma modulation technique that lowers output noise and total harmonic distortion plus noise (THD+N) when compared to conventional pulse width modulators.

The LM4667 is designed to meet the demands of mobile phones and other portable communications devices. Operating on a single 3V supply, it is capable of driving 8Ohm transducer loads at a continuous average output of 450mW with less than 1% THD+N. Its flexible power supply requirements allow operation from 2.7V to 5.5V.

The LM4667 is available now in 9-bump micro SMD packaging and is priced at $0.48 in 1,000-unit quantities.

More information on the LM4667 is available at National LM4667.

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