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FDC2212: Choosing Inductor

user5866401
Intellectual 430 points
Part Number: FDC2212

Hello;

I did some test with 10uH, 22uH and 68uH inductors. All inductors are tested with 39pF, 100pF, 270pF,

SRF of inductor is 19mHz. All inductor is shielded.

When the Q is big, measurement is better. When L is increase, Q is increase.

I see that 10uH is better.

Which other parameter of inductor effect on measurement?

which type of inductor must be chosen; multilayer or wirewound?

Best Regards.

  • 0
    TI__Genius 17440 points
    Hello,

    When you say that the 10uH inductor is better, can you clarify what you mean? What is improved?

    Also note that increasing L does not necessarily increase Q, because Rs will change as well. Two inductors with the same inductance value can have significantly different Rs values.

    When selecting an inductor, the most important constraints are the FDC2212's sensor frequency range and drive current range. As long as the LC tank's resonant frequency is between 10kHz-10MHz and the sensor oscillation amplitude is between 1.2-1.8V, the inductor should work for the system.

    Best Regards,
  • 0 in reply to Kristin Jones93
    Intellectual 430 points
    Hello;

    Measurement range is 42pF to 100pF
    When I use 10uH, the measurement value is correct. when I use 22uH, the measurement value is correct only 42pf to 75pF.
    *single ended configuration is used.

    Is there any effect on measurement of inductor's Rdc value?(fdc's INxA output is sunisoidal )

    Best Regards.
  • 0 in reply to user5866401
    TI__Genius 17440 points
    Hello,

    The Rp value (at the sensor's resonant frequency, not DC) definitely impacts the INxA waveform. The sensor drive current should be set so that the sensor oscillation amplitude is between 1.2-1.8V. In this range the SNR will be maximized. This application note is for inductive sensing devices, but the drive current configuration process is the same. It should help you verify that your sensor oscillation amplitude is set correctly through your full capacitance range.

    application note: www.ti.com/.../snoa950.pdf

    Best Regards,
  • 0 in reply to Kristin Jones93
    Intellectual 430 points
    Hello;

    Thank you for answers.

    Inductor value cahnge 10.47uH to 10.56uH when frequency change 1mHz to 5mHz.

    product.tdk.com/.../info

    How this effect may be reduced?

    Best Regards.
  • 0 in reply to user5866401
    TI__Genius 17440 points
    Hello,

    As Clancy has answered your question in another thread, I am marking this thread as resolved.

    Other thread: e2e.ti.com/.../800027

    Best Regards,