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LDC Unstable measurement value

na na78
Guru 16770 points
Other Parts Discussed in Thread: LDC1614EVM

Hi

We are using the minimum coil N which is included in LDC reference cols board.

We added a series fixed inductor whose inductance is 10uH.

A capacitance of sensor capacitor is 330pF.

We evaluate this sensor with LDC1614EVM, it doesn't seem to work properly.

The measured value is always continued to increase or decrease at the time of measuring.

The sensor and EVM remain fixed and they don't move.

What do you think the cause?

Best regards

  • 0
    TI__Genius 13650 points
    Hi Na Na,

    Perhaps the series inductor that you chose isn't ideal for this application. I recommend the following procedure to find the root cause:

    1. Are you using a C0G/NP0 type sensor capacitor? If not, please swap out the capacitor to this type.

    2. How much does the output code drift by?
    - Can you check with the GUI over a few minutes and calculate the code delta in ppm of full scale?
    - What is the code change compared to the desired signal change (when you move your target from its minimum position to its maximum position)
    Perhaps the code drift is so small that it can be ignored while still meeting your system specification.

    3. To find the root cause, remove coil N so that you only have your 10uH + 330pF circuit. This should oscillate with minimal drift.

    4. If your circuit still does drift significantly, you may want to try a different inductor. For example, CMH322522-180KL has worked very well for me to give stable oscillation. Its value is too large for your application, but it should show if your issue is caused by inductor choice or by something else.