Santa Clara, Calif. 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 I²C control all into a single, space-saving package. The full-featured LM4931 contains a stereo I²S 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 I²C or serial peripheral interface (SPI) digital control interface. I²C/SPI control allows selection of a variety of operating modes, volume control, and other performance functions.
National's LM4859 is an integrated audio subsystem that operates on a 2.7-5.5 V supply. It combines a stereo speaker amplifier that delivers 495 mW per channel into an 8Ω load, and a stereo headphone amplifier that delivers 25 mW per channel into a 32Ω load with a 3.3-V power supply. In addition, the LM4859 routes and mixes the stereo and mono inputs into 16 distinct output modes using a simple I²C compatible interface. Other features include an ultra-low current shutdown mode and thermal shutdown protection.
National's LM4931 is an integrated audio subsystem that supports voice and digital audio functions. The full range I²S music path features a signal-to-noise ratio of 86 dB with an 18-bit, 48 kHz input. The high efficiency Class D speaker amplifier delivers 470 mW into 8Ω and the headphone amplifier delivers 26 mW root means square (RMS) to a 32Ω single-ended stereo load with less than one percent total harmonic distortion plus noise (THD+N) with a power supply of 3.3 V. Additionally, the LM4931 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 I²C or SPI compatible interface. Simple I²C 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 now in a 28-lead LLP packaging and is priced at $1.80, and the LM4931 is available now in a 42-bump micro SMD packaging and is priced at $4.15, both in 1,000-unit quantities.
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