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FDC1004EVM: FDC1004EVM: Some errors occurred when using CAPDOC setting

kim junho
Prodigy 10 points
Part Number: FDC1004EVM
Other Parts Discussed in Thread: FDC1004

Hi Ti team,

I need some help and want to get adivse about measuring capacitance with FDC1004EVM

I found some errors when I used with CAPDOC,

I tested FDC1004EVM with TI's Sensing solution EVM GUI

Measured Capacitor is 27pF(C class) Samsung MLCC 2012(0805) Size

And I tested CIN2 to Ground mode and Single-ended measurement

And here's my problem

When I set CAPDOC code less than 8, the Measured Capacitance is 28.56pF

but when I set CAPDOC code more than 9 the Measured Capacitance is 23.05pF

I can found this problem in another circumstance(Change CAPDOC 27 to 28)


I know measuring real value is not recommended but there's some gaps between real capacitance value and measured value with FDC1004 EVM

I'm going to measure RFIC resonant capacitance and get standard deviation graph so, I don't need real value but I want to know why this error occurred.

Last, I have a question about measuring capacitance

Is it okay to measuring RFIC resonant cap with FDC1004? do you have another recommadation?

As always, Thank for your support

Regard.

Junho

  • 0
    TI__Mastermind 40295 points

    Junho,

    Thank you for your inquiry and your interest in TI products.

    Just to confirm, are you trying to measure an absolute capacitance, or a change in capacitance?

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Prodigy 10 points

    Hello, John

    Thank you for your reply

    I'm trying to measure an absolute capacitance.

    If the gaps between absoulte capacitance and measured value are consistent, and it's okay

    because i want to get reference graph of my product 

    I think, build the measuring capacitance system with FDC1004 is more convenience than using LCR meter product

    So I tested with FDC1004EVM

    But if you have any other suggestions, I would be glad to hear them

    Regards,

    Junho

  • 0 in reply to kim junho
    TI__Mastermind 40295 points

    Junho,

    I have never tried this before, but it might be worth making a series of measurements of your fixed capacitor with different CAPDAC settings.
    This approach attempts to emulate a shifting capacitance by changing the CAPDAC, instead of the sensor.
    Some kind of  average or curve-fit of the data may be able to predict a nominal or average number close to the actual cap value, or perhaps a predictable error you could use as a "fudge-factor".

    Another approach might be to make a measurement - or series of measurements - without the fixed capacitor in place, and then use that as baseline condition for comparison when the capacitor is actually in place.

    Again, I have never tried this before, so I have no idea if it will work, but it may be worth a try.

    If your try this approach, please let me know how it goes.

    Regards,
    John