I'm using an FSA9485 Multimedia Switch (MMS) for audio recording via USB headset. So far, just noise is recorded...so I'm wondering if the MICBIAS is working correctly.
The MMS schematic shows MICBIAS applied on the codec side of the MMS, which is how we've implemented it:
The headset MIC pin is connected to VBUS_IN of the micro USB connector. I've measured voltage at VBUS_IN, and don't see any amount of bias voltage. At the codec, MIC/MICBIAS is roughly 1.2-1.4V.
Will an "ear bud" style microphone work with no bias? I presume the bias voltage should be present at the connector so that it can properly bias the headset mic.
EDIT: Turns out I wasn't contacting the micro USB VBUS or GND pin properly with my multimeter and the 1.4V bias is present at the connector. It's working properly for me with the bias.