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LDC2112: LDC 2112 Ccom

Simon Scheerer
Prodigy 20 points
Part Number: LDC2112

Dear TI team,

I have one question to the Ccom value.

In your excel sheet I got a value Ccom min > 2.15 nF and Ccom max < 26.88 nF.

Actually we are using a Ccom with a value of 2.2 nF. Is this to be seen critically?

Furthermore, if we are to close at the minimum what kind of effects will we get?

Thank you in advance.

Best regards 

Simon

  • +1
    TI__Mastermind 33170 points

    Simon,

    As long as Ccom is within the suggested range given in the tool, everything should be okay.
    Please note some suggestions for the PCB layout for Ccom are given in section 10.1 of the LDC2112 datasheet:
    ---
    The COM pin must be bypassed to ground with an appropriate value capacitor. For details of how to choose the
    capacitor value, refer to Setting COM Pin Capacitor. CCOM should be placed as close as possible to the COM
    pin. The COM signal should be tied to a small copper fill placed underneath the INn signals. The INn signals
    should stay clear of other high frequency traces.
    ---

    Pease let me know if you have any questions.
    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Prodigy 20 points

    Hello John,

    the Ccom was implemented by the suggestions from the datasheet.

    But if we are talking about tolerance, what happens if the Ccom is out of range because it depends on the tolerances?

    Can there occur any kinds of effects in this way?

    Best regards

    Simon

  • 0 in reply to Simon Scheerer
    TI__Mastermind 33170 points

    Simon,

    The most likely outcome is that device sensitivity and detection will be degraded, but we can't say by how much.
    There may be other aspects of the device behavior that will not follow the data sheet specs & descriptions, so there is risk there as well.

    I know these are vague comments, but we simply can't offer much data or guidance on how a device will operate outside of the published values & limits. 

    Regards,
    John