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EDN -- 04.25.96 Audio-amp IC serves both headset and microphon EDN Staff - April 25, 1996
Out in Front:April 25, 1996
Audio-amp IC serves both headset and microphone
For hands-free communications systems, such as mobile phones, desktop conference phones, and portable computers, the LM4830 from National Semiconductor includes functions for both audio directions. The 24-lead IC contains a power amplifier for a speaker, a headset amplifier, and a microphone preamp. The power amplifier delivers as much as 2W into a bridged, ungrounded, 4 Ohm load with distortion less than 1%. THD is less than 0.1% with 1W continuous output. The headset amplifier provides as much as 100 mW into a 32 Ohm grounded load. You control the volume digitally using a 4-bit code, with 15 steps of 2 dB each, for a total gain range of 30 dB. The LM4830 lets you select between two microphone inputs, useful when switching between an internal speaker/microphone system and an external handset microphone. The microphone preamp channel also has a separate buffered line-level output that can drive capacitive loads. The 2.7 to 5.5V, single-supply IC draws 11-mA typical quiescent current and is available in SO and DIP packages. Price is $2.65 (1000).—by Bill Schweber National Semiconductor Corp, Santa Clara, CA. (800) 272-9959, http://www.national.com.
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