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National expands feature sets on audio subsystems

Posted: 05 Nov 2004 ?? ?Print Version ?Bookmark and Share

Keywords:national semiconductor? lm4859? audio amplifier? lm4931?

National Semiconductor Corp. launched two boomer audio subsystems that provide a wide variety of features for cellular phones and portable applications.

The LM4859 compact subsystem integrates the audio amplifiers, volume control, mixer, power management control, 3D sound enhancement and I?C control all into a single, space-saving package. The full-featured LM4931 contains a stereo I?S digital-to-analog converter (D/A converter), on-board phase-locked-loop (PLL), a voice band codec, stereo headphone amplifier, Class D mono speaker amplifier, microphone pre-amplifier and sidetone generator, all with an I?C or serial peripheral interface (SPI) digital control interface. I?C/SPI control allows selection of a variety of operating modes, volume control, and other performance functions.

The LM4859 is an integrated audio subsystem that operates on a 2.7V to 5.5V supply. It combines a stereo speaker amplifier that delivers 495mW per channel into an 8? load, and a stereo headphone amplifier that delivers 25mW per channel into a 32? load with a 3.3V power supply. In addition, the LM4859 routes and mixes the stereo and mono inputs into 16 distinct output modes using a simple I?C compatible interface. Other features include an ultra-low current shutdown mode and thermal shutdown protection.

The LM4931 is an integrated audio subsystem that supports voice and digital audio functions. The full range I?S music path features a signal-to-noise ratio of 86dB with an 18bit, 48kHz input. The high efficiency Class D speaker amplifier delivers 470mW into 8? and the headphone amplifier delivers 26mW root means square (RMS) to a 32? single-ended stereo load with less than one percent total harmonic distortion plus noise (THD+N) with a power supply of 3.3V. Additionally, the device has advanced circuitry to reduce power consumption and controller overhead, and to eliminate pop and click noise.

Unlike hard to use audio codecs that require sophisticated software development for operation and control, both the LM4931 and LM4859 use a standard I?C or SPI compatible interface. Simple I?C or SPI commands are used to set one of the operating modes and volume level for any given audio amplifier. The operating modes are predetermined to cover all of the functional needs required in portable applications. The LM4931 has 10 preset operating modes, while the LM4859 has extra modes for the 3D feature for a total of 16. These modes not only make the devices easy to use but also allow the user to turn off unused amplifiers to optimize system power management.

The LM4859 is available in a 28-lead LLP packaging and is priced at $1.80, and the LM4931 is housed in a 42-bump micro SMD packaging and is priced at $4.15, both in 1,000-unit quantities.

- Bettyann Liotta

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