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FDC2212: Why does FDC2212 not work steadly

Dengkuan Sun
Prodigy 240 points
Part Number: FDC2212

Tool/software:

Hi Experter,

I am using FDC to detect the proximity. I met some issues. Can you help them?

My sensor is cylindrical copper foil. And it is connected to IN0A. The issues are describled as the lists

  1. When the FDC is powered on, FDC can measure a frequecy A. Normally, when a person is close to the sensor, the frequency should be decreased. But, sometimes, the measured frequency will be increased. And, I must power off the FDC in order that FDC work normally. Can you explain this?
  2. I followed John's suggestion to add a buffer circuit as the active shielding. However, when I connected the shielding, the measred value is disturbed so that I cannot get the normal value. Therefore, how to fix this?
  3. About the capacity sensor, is there any document to describle how to design. How to configure the circuir of FDC?

Thanks

  • 0
    Prodigy 240 points

    Additional Question: When the frequency is about 3.2 MHz, how to configure the register of Input Deglitch Filter? Is it 3.3MHz or 10MHz?

  • 0 in reply to Dengkuan Sun
    TI__Mastermind 40295 points

    Dengkuan,

    1. With nearby objects, the sensor frequency can increase depending on the object's properties, such as if it is grounded or not.
    2. The active shield driver circuit needs to be able to reproduce the sensor's signal on the shield without any time delay or difference in amplitude (with respect tot eh sensor waveform). This can be challenging for the driver amp if the shield has a lot of capacitance. Please look for any difference between the sensor waveform and the active shield waveform.
    3. We don't have any documents yet for FDC2x1y device settings.

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Prodigy 240 points

    For the second point, It is realy diffecult because the shield cannot keep the same capacitance for the different sensor. Do you have any suggestion about designing the driver circuit in order to keep the robustness?

    For the input deglitch filter, do you have any suggestion? Currently, the frequency is about 3.17MHz.

  • 0 in reply to Dengkuan Sun
    TI__Mastermind 40295 points

    Dengkuan,

    We don't have a reference design for a shield driver, but we should.
    A higher-power op amp should work, but please be sure to use one that is rated for driving high capacitances.

    The 3.3MHz deglitch filter should work for the sensor frequency you are using.

    Regards,
    John