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FDC1004EVM: Can I ac couple the CINn inputs to isolate them from a 200V DC offset on a variable capacitor I am trying to measure.

Dean Tipple80
Prodigy 30 points
Part Number: FDC1004EVM
Other Parts Discussed in Thread: FDC1004, FDC2214

I have a system where there is a MEMS membrane that is moved by varying the DC voltage applied.  I want to look at the capacitance from the membrane to GND as the DC voltage applied to the membrane is stepped from 0 to 200V.  I would like to AC couple the membrane to the CIN with a fixed capacitor <100pF so it can be nulled out with the offset dac.  The change in capacitance will be a few pF as the membrane voltage is stepped from 0 to 200V. I want to test this with the FDC1004EVM if it has a reasonable chance of success.

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    TI__Genius 17440 points

    Hello,

    The FDC1004 will not be able to properly measure the capcitance of this system, because it drives the electrodes with a stepped DC waveform, not an AC waveform. You might be able to use this approach with the FDC2214, which drives the sensor with an AC waveform.

    Best Regards,