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FDC2114: Calculation of sensor frequency out of conversion results

Andrea Bierler
Prodigy 90 points
Part Number: FDC2114

Hello,

I am using the FDC2114 in single ended sensor configuration. For the relationship between the sensor frequency and the conversion result in the DATA register, I find 2 formulas in the data sheet: formula (1) on page 15 and formula (8) on page 19. Can you please confirm which formula to use for calculating the sensor frequency (and therefore the sensor capacity)?

Best regards,

Andrea

  • 0
    TI__Expert 3435 points

    Hi Andrea,

    Those equations are interrelated. If you know Freq, you can calculate Data- and vice versa.

    You can get the Data from a register directly. You can use that value to calculate the Capacitance. 

    In other words, all these represent the same information in different formats. 

    Regards

    Sharath.

  • 0 in reply to Sharath Vallamkonda
    Prodigy 90 points

    Hello Sharath,

     

    thank you for your response!

    I want to get the Data from the corresponding register and calculate the capacitance.

    My understanding is: I need to calculate the sensor frequency fSENSOR first and use the result to derive the capacitance. For calculating the sensor frequency out of the Data register, I find equation (1) (which can be solved for fSENSOR) and equation (8) in the data sheet. In my opinion, these equations coincide if CHx_OFFSET = 0, OUTPUT_GAIN = 0 and CHx_FIN_SEL = 1. But for different register configurations, equation (1) and equation (8) do not coincide.

    Can you please explain if I misinterpret something?

     

    Best regards,

    Andrea

  • 0 in reply to Andrea Bierler
    TI__Expert 3435 points

    Hi Andrea,

    Yes, it is a bit confusing. You can think of Eq 1 as a simplified version of Eq 8. As you said, both are equal when CHx_FIN_SEL=1 and CH offset =0. You are correct, fSENSOR needs to be calculated from equation 8 and Csensor can be calculated from the EQ7.

    Let us know if you have any more questions.

    Regards

    Sharath.