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Space-saving Class D audio amplifiers

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article image Housed in micro SMD packages.

NATIONAL Semiconductor, represented by Arrow Electronics , introduced two new high-efficiency Class D audio amplifiers to its expansive Boomer portfolio.

These new audio amplifiers are housed in tiny micro SMD packages and feature externally configurable gain for space savings and flexibility in design.

Additionally, they feature a low power consumption shutdown mode for extended battery life. These two parts are ideal for applications such as cellular phones, PDAs and other portable electronic devices.

National Semiconductor's LM4670 is a 3W and the LM4671 is a 2.5W fully integrated single-supply, high-efficiency switching audio amplifier. They feature innovative modulation schemes that eliminate the output filter used with typical switching amplifiers.

Eliminating the output filter reduces external component count, simplifies circuit design and reduces board area. The LM4670 processes analogue inputs with a delta-sigma modulation technique that lowers output noise and total harmonic distortion (THD).

Due to its high output power, the LM4670 is optimised for ultra high-power push-to-talk, push-to-talk over cellular (PoC) and hands-free use.

The LM4671 processes analogue inputs with a pulse width modulation technique that results in lower output noise, making it well suited for earpiece/receiver applications as well as normal high-power ringer and hands-free operation.

Operating on a single 5V supply, the LM4670 and LM4671 are capable of driving a 4 Ohm speaker load at a continuous average output of 2.3W with less than one percent total harmonic distortion plus noise (THD+N).

Flexible power supply requirements of these parts allow operation from 2.4V to 5.5V. The LM4670 and LM4671 have high efficiency with speaker loads compared to typical Class AB amplifiers.

With a 3.6V supply driving an 8 Ohm speaker, the amplifier's efficiency is 88 percent at 600mW output power. Additionally, the LM4670 and LM4671 feature a low power consumption shutdown mode.

Shutdown may be enabled by driving the shutdown pin to a logic low level. Gain is externally configurable to allow the user to sum multiple inputs while optimising the gain for each source.

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