• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 30 subscribers
  • Views 226 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

FDC1004: Steps in capacitance between 40C and 50C

Franz Schellhase
Expert 3605 points
Part Number: FDC1004

Hi Team.

A customer is using this device with 3 electrodes. When they are putting their PCB in a climate chamber they see jumps in capacity on the electrodes at approx. 40C and 50C. Is there a phenomenon you are aware of that could cause this?

Examples of steps in capacitance:

  • Electrode 2:
    • 0.18pF to 0.16pF at 40C
  • Electrode 3:
    • 0.29pF to 0.26pF at 50C

Thank you,

Franz

  • 0
    TI__Mastermind 40295 points

    Franz,

    Are the variations you mentioned from the sensor capacitance at room temp to the higher temp?
    1. For example, for Electrode 2 is 0.18pF the sensor capacitance at room temp, and 0.16pF the capacitance at 40C?
    2. Or do those two numbers represent the variation in sensor capacitance at 40C?

    Temp variation of the offset over the range -40C < T < 125C is given in the data sheet as TcCoff = 46fF,.
    If it is option (1) above, it looks like their variations (20fF-30fF) are within this range

    If it is option (2) is it possible for them to temp test just their sensors and leave the PCB at room temp?

    regards,
    John

  • 0 in reply to John Miller - Sensing
    TI__Expert 3605 points

    Hi John,

    It looks like the following. Sorry, I mistook electrode 2 and 3 in my initial description.

    As you can see the capacitances take a step at approx. the mentioned temps. So it is not a gradual drift over temp. I would thus dismiss explanation 1 and follow up if they can do the temp tests with PCB at room temp.

    Best regards,

    Franz

  • 0 in reply to Franz Schellhase
    TI__Mastermind 40295 points

    Thank you Franz.
    we will wait for an update from the customer's experiments.

    Regards,
    John