Other Parts Discussed in Thread: BQ500212A
I'm modifying an existing production design to use the bq500211A (used bq500212A, changed due to sourcing issues). We have an issue with the demodulation circuit's common mode voltage. We're using the same demodulation circuitry, and expect it to be biased to 1.5V.
The common mode voltage frequently appears to be ~800mV. I've confirmed the voltage divider circuit is correct by removing the 10Ω resistor connecting the circuit to the COMM_A+ and COMM_B+ pins.
Somehow the COMM+ pins are pulling the common mode voltage down. The voltage will be correct at +1.5V for stretches lasting minutes, then get pulled down. I've also seen it cut in an out, as seen in the scope trace. I've verified the resistance and capacitance of all components in the demodulation circuit. Any help or context on the COMM circuitry inside the bq500211A would greatly help. Thanks!
