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National Boomer audio subsystems suit portable apps

Posted: 10 Nov 2004 ?? ?Print Version ?Bookmark and Share

Keywords:national semiconductor? boomer audio subsystem? lm4859? lm4931?

National Semiconductor Corp. recently launched two Boomer audio subsystems that provide a 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. Meanwhile, the full-featured LM4931 contains a stereo I?S DAC, 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 SPI digital control interface. I?C/SPI control allows selection of a variety of operating modes, volume control, and other performance functions.

"National's LM4859 and LM4931 integrated audio subsystems provide everything our customers need," commented Gary Adrig, the company's marketing director for its audio products group. "These audio subsystems give customers a huge feature set in a very compact space. By integrating all of the features that a customer might need into a single package, the LM4859 and LM4931 provide space and system cost savings without sacrificing performance."

Operating on a 2.7V to 5.5V supply, the LM4859 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. Additionally, this device routes and mixes the stereo and mono inputs into 16 distinct output modes using a 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?, while the headphone amplifier delivers 26mW root means square 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. In addition, the LM4931 has advanced circuitry to reduce power consumption and controller overhead, and to eliminate pop and click noise.

Unlike other 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, National said. 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 company added.

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 $3.99, both in 1,000-unit quantities.

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