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LDC1614: Inductance Shift

Janine Lin
Expert 2190 points
Part Number: LDC1614

Dear Clancy and Bala

By looking at the GUI, why is it inductance will shift even my target is fix?

Please see figure and short video clip below.

  • 0
    TI__Mastermind 23810 points
    Janine,

    Can you show the raw data output in this graph instead of the inductance? It's a little easier for us to debug that way.
  • 0 in reply to Clancy Soehren
    Expert 2190 points

    Dear Clancy,

    Here is the raw data output.

  • 0 in reply to Janine Lin
    Expert 2190 points

    Dear Clancy

    Please see the video clip below. This is the output raw code.

  • 0 in reply to Janine Lin
    TI__Mastermind 23810 points
    Janine,

    It looks like you are seeing a 1 LSB of resolution step (note that depending on frequency and RCOUNT, the output codes will often not have sequential steps). This is normal behavior. If you increase RCOUNT, you should see the step size decrease (meaning that resolution increases).

    The output may look "noisier" but the peak-to-peak output code variation should reduce.
  • 0 in reply to Clancy Soehren
    Expert 2190 points

    Thank u Clancy. I used Rcount code of 65535 (2^16).

  • 0 in reply to Janine Lin
    Expert 2190 points

    Dear Clancy

    Which delta value must to follow? I'm testing our second sensor coil, as i know to determine the sensing range is 10x noise floor delta, with target and without target. In the data streaming, as 

    what you said it is 1 LSB of resolution step. But i am confused which delta value will take as a reference, because it changes  even without target.

    Please see the video clip below. This is when "no target".

  • 0 in reply to Janine Lin
    TI__Mastermind 23810 points
    Janine,

    What you are currently measuring is the noise floor. My apologies for using the "1 LSB" term, which I used in a confusing manner. One resolution step in this case is multiple LSBs (which you can see by looking at the delta when the value is oscillating between two specific values). To improve the resolution, increase RCOUNT (which increases the sampling time).
  • 0 in reply to Clancy Soehren
    Expert 2190 points

    i already set the RCount in a higher value which is 65535. I am confused which delta value to follow as a reference (no target).

  • 0 in reply to Janine Lin
    TI__Mastermind 23810 points
    If you are trying to calculate the noise floor, then use the worst case delta. If your signal is 10 times stronger than that, then the design is reasonably robust.
  • 0 in reply to Clancy Soehren
    Expert 2190 points
    ok Clancy. Got it. Thanks~