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2.1W Differential Input, BTL Output Stereo Audio Amplifier with RF Suppression and Shutdown
National Semiconductor

The LM4884 features differential stereo inputs, BTL (bridge-tied load) outputs, and four externally selectable fixed gains. The LM4884 also features proprietary internal circuitry that suppresses the coupling of RF signals into the chip. This is important because certain types of RF signals (such as GSM) can couple into audio amplifiers in such a way that part of the signal is heard through the speaker. The RF suppression circuitry in the LM4884 makes it well-suited for notebook and portable applications in which strong RF signals generated by an antenna from a PC wireless card or a cellular phone may couple audibly into the amplifier. Operating on a single 5V supply, the LM4884 delivers 1.2W, 1.9W, or 2.1W (typ) of output power to an 8, 4, or 3 BTL load (Note 1), respectively, with less than 1% THD+N. The LM4884's gain is selected using two digital inputs. The nominal gain values are 6dB, 10dB, 15.6dB, and 21.6dB. Other features of the LM4884 are that it delivers high-quality output power from a surface-mount package, requires few external components, has an active-low micropower shutdown mode input, and has thermal shutdown protection.

???Improved RF immunity, by up to 28dB over previous designs (such as the LM4874) in selected applications.
???Fully differential input and output
???Internal gain set: 6dB, 10dB, 15.6dB, and 21.6dB
???Improved "click and pop" suppression
???Thermal shutdown protection circuit
???Ultra low current micropower shutdown mode
???3.0V to 5.5V operation
???Available in space-saving exposed-DAP TSSOP package

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