A better boom

has introduced the

stereo audio subsystem, the industry's first subsystem to incorporate digital and analogue input paths for multimedia, smart and voice-over-Internet procotol (VoIP) phones. National says the Boomer audio power amplifiers provide high quality output power with a minimal number of external components.

"Cell phone manufacturers use a combination of digital and analogue sources in their designs," said Mike Polacek, vice president of National Semiconductor's Audio group. "For example, the output of an MP3 decoder may be digital, while an FM radio module's output may be analogue. This flexibility, combined with the on-chip features, helps engineers save components, board space, cost and design time."

National said in a statement that the LM4934 audio subsystem integrates audio amplifiers, volume control, a mixer, power management control and National's 3D stereo sound-enhancement technology into a new, 3.3 mm by 3.9 mm, 42-bump micro SMDxt package. The 3D capability makes it easier for listeners to hear music more clearly through the phone by broadening the sound field of the closely placed speakers.

The LM4934 offers an I2S digital input and three analogue inputs, which National says eliminates the need for an external digital-to-analogue converter (DAC) and a multiplexer integrated circuit. Operating on a 3.3V supply, the single-chip LM4934 combines a stereo speaker amplifier delivering 500 mW typical per channel into an 8-Ohm load and a stereo headphone amplifier delivering 30 mW typical per channel into a 32-Ohm load. The chip features a 25 mW mono earpiece output and a separate line out to drive external audio devices.

The on-board phased-lock loop (PLL) reportedly simplifies the customer's selection of a clock frequency (from 8 MHz to 24 MHz) and saves cost by eliminating the need for an external crystal oscillator. The entire chip is controlled through 25 separate I2C compatible registers for maximum flexibility of routing inputs and outputs through the two-wire interface. In addition, the LM4934 routes and mixes the stereo and mono inputs into multiple, distinct output modes using a simple I2C compatible interface.

The LM4934, available now in a standard 42-bump micro SMDxt package, is priced at $3.80 in 1,000-unit quantities. A lead-free package will be available in early 2006.