Mixed-signal chip combines audio, power

Wolfson Microelectronics has introduced the AudioPlus product line, which will combine the company's expertise in high-quality audio for portable products with a power-management subsystem. Wolfson has combined functions from both of these domains in a single mixed-signal chip. The WM8350, the first product in the family, comprises an audio codec with a suite of regulators and dc/dc converters that will meet all of the power-management needs of a typical portable product, such as a mobile handset or media player. On the audio side, a high-fidelity audio codec has mixing capabilities, pop and click suppression, and signal/noise performance of 98 dB for its DAC at −84-dB THD (total harmonic distortion). The audio chain's ADC achieves SNR (signal-to-noise ratio) of 95 dB at −80 dB THD.

The chip has six analog inputs, two stereo analog outputs, and two monophonic line outputs; it also features on-chip headphone amplifiers that drive 20 mW into 16Ω with THD of −70 dB. Power-management functions switch and regulate multiple voltage lines. You can program four 2-MHz dc/dc step-down (buck) converters to provide 0.85 to 3.4V in 25-mV steps. The converters yield peak efficiency of more than 90%, and they need only a small external inductor and capacitor per line. To generate voltage above the battery line—for display backlighting and for the 5V necessary for USB—two 1-MHz boost converters also achieve more than 90% peak efficiency.

You can program four on-chip, 150-mA, low-noise, low-dropout regulators over 0.9 to 3.3V in 50- or 100-mV steps, depending on the version. To handle the lithium battery that typically powers the class of products that Wolfson has in mind for this chip, a single-cell charger—programmable for different cell voltages—has trickle and fast-charging modes. The charger finds its supply from USB or ac/dc source, as available, and allows product operation while charging an empty battery.

The chip has 13 I/O pins that you can use to control system functions: You can program, either at start-up or during operation, all of the outputs to set power-up and -down sequences using a dedicated onboard controller. The chip occupies a 129-pin, 7×7-mm BGA package with a 0.5-mm ball pitch. Wolfson acknowledges that, if you use all of the regulation functions at rated levels, the chip will dissipate 1 to 2W but says that you can use all of the lines together and stay within the chip's fully protected operating zone.

Combining these mixed-signal functions on one chip can save you 25% in external-component count and 50% in board area, the company says. The chip's designers synchronized audio and dc/dc-converter clocks to avoid on-chip-interference effects, but Wolfson claims that this step turned out to be largely unnecessary. Wolfson's expertise in physical and substrate phenomena on mixed-signal processes minimized unwanted effects.