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Original question:

FDC2214 Drift over time

FDC2214: FDC2214 Drift over time

servet ayok
Prodigy 95 points
Part Number: FDC2214
Other Parts Discussed in Thread: FDC2212

Hello,

You said that capacitance drift is due to temperature drift of the board.

I connected a capacitive sensor to channel 0 and nothing is connected to channel 1 on FDC2214 EVM. 

I expected to see capacitance drift on both channels due to temperature change.

However, CH0 drifted 100fF and CH1 drifted 5fF over time.

I guess huge drift on CH0 is not due to temperature change.

What might be the problem?

  • 0
    TI__Genius 17440 points
    Hi Servet,

    The sensor itself can be a large source of capacitance drift over temperature. The sensor is generally a large area of copper, and its electrical characteristics will change with temperature. In addition, the spacing between the layers of the board can change with temperature. The combination of the copper's changing electrical characteristics and its changing proximity to other layers can yield significant capacitance drift over temperature. I believe the drift you are seeing is still due to temperature change.

    Regards,
  • 0 in reply to Kristin Jones93
    TI__Genius 17440 points
    Hi Servet,

    I haven't heard from you in a few days. If you have any followup questions or additional information to share, please reply so we can continue the discussion. If not, I will close this thread.

    Regards,
  • 0 in reply to Kristin Jones93
    Prodigy 95 points
    Hello Kristin,

    I have another serious problem.

    I start reading values from FDC2212, I turn off the power supply, wait for 2-3 seconds and turn on power supply again, begin to read the values.

    The problem is, the values before turning off and after turning on are quite different like 35047488 and 34297980 where I am looking for 10000 value change.

    What could be the problem and any suggestions to solve this huge shift?

    Regards.
  • 0 in reply to servet ayok
    TI__Genius 17440 points

    Hi Servet,

    When the FDC2212 is powered down, it will reset all of its registers to default values. If you have customized any register settings for your application, you will need to rewrite all of them after you power the device back on. The RCOUNT register is one of the most likely causes of the differences you are seeing. The longer you give the FDC2212 to measure the sensor frequency, the more accurate it will be. 

    Regards,