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FDC2214 External Multiplexers or Alternative Recommendation

ErnestHanks_55
Intellectual 460 points
Other Parts Discussed in Thread: FDC2214

Hello TI,

1) Buried in the FDC2214 datasheet on Page46, Section 10.3, the datasheet claims: "The FDC does not support hot-swapping of the sensors. Do not hot swap sensors, for example by using external multiplexers."

Can you please elaborate on what this means and why it is not supported? Is it not supported even if I disable the device prior to external multiplexing?

2) Does TI have a recommended configuration for what I'm trying to implement? I'm attempting to measure the capacitance difference between 2 DISCRETE capacitors of nominal 50pF and 500pF value with good precision (better than 1%) for calibration purposes. There are two modes of operation

MODE1: the capacitors need to be connected in the Circuit and NOT the FDC2214. The FDC2214 cannot be connected in the circuit during normal operation.

MODE2: the capacitors need to be hooked up to the FDC2214 only.

I was planning on doing this with external multiplexing until I saw the above comment without a good explanation. Bandwidth/timing is not an issue; this can be done very slowly.

Here is my sketch of what I was planning to do.

  • 0
    TI__Expert 8050 points
    Hello ErnestHanks,

    The sentence is really an alert only and the wording is probably too strong. In some rare circumstances, hot-swapping the sensors may not work reliably if there was too much charge. For most applications, it should work fine.

    Regards,
    Yibo