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Audio and stereo amp ICs extend Boomer portfolio for portables

Santa Clara, Calif.&#8212National Semiconductor's LM4941 audio amp and LM4985 stereo amp additions to the company's Boomer line of Class AB amplifiers, in the industry's smallest micro SMD package (0.4 mm pitch), improves performance in space-constrained portable and wireless applications.

The LM4941 Class AB, 1.2-watt audio amplifier integrates the company's RF suppression circuitry, which reportedly provides up to a 20 dB improvement over existing designs in minimizing noise that finds its way into the audio stages. The differential amplifier has a quiescent current of just 1.7 mA (for a 5-volt supply).
It features 0.04 percent total harmonic distortion plus noise (THD+N), typical power supply rejection ratio (PSRR) of 95 dB at 217 Hz and a signal-to-noise ratio (SNR) of 108 dB at 1 kHz. The amp also provides a mono speaker output.

The LM4985 stereo headphone amp has a 32-step, non-linear volume control that's compatible with the I2 C bus. The amp, with a quiescent current of just 3 mA, delivers 135 mW per channel of continuous average power into a 16-ohm load. The LM4985 may be applied as either a capacitive-coupled or output capacitor-less (OCL) device.

The LM4985 delivers 68 mW per channel of continuous average power into a 16-ohm load, or 38 mW per channel into a 32-ohm load with 1 percent total harmonic distortion, when operating in the OCL mode. Its I2 C compatible volume control allows the user to set the gain from 18 db to -76 db. At very low volumes the step sizes are large. At high volumes, where the human ear can discern much smaller level changes, step sizes are small. The amp also has a PSRR of 77 dB at 217 Hz (OCL operation).

Both chips will work without bootstrap capacitors and feature an internal thermal shutdown protection mechanism. Their advanced pop and click circuitry eliminates noises that would otherwise occur during turn-on and turn-off transitions.

The LM4985 is priced at $1.46 each and the LM4941 is priced at 62 cents each, both in 1,000-unit quantities. Click here and here for additional information on the devices and to order samples. Click here for the company's on-line seminars on audio amplifiers.

National Semiconductor , 1-800-272-9959, www.national.com

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