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[LDC1612] Read wrong Inductive value

Kaka
Guru 24520 points
Other Parts Discussed in Thread: LDC1612, LDC1614EVM

Hi Community member,

Please provide some advice for the following phenomenon which we had met.

[Phenomenon]

　When we read the CH0 data of LDC1612, the value rarely showed the 0xFFFFF.

I know that the LDC1612 will show this value if there is not mounted the coil for channel of LDC1612.

But we did not remove this coil. So, what is cause of this?

If you have any question or need more question, please let me know.

Best regards.

Kaka

  • 0
    TI__Genius 9300 points
    Hello Kaka,

    What value does it show during normal operation?
    Can you reliably reproduce this phenomenon?
  • 0 in reply to Evgeny Fomin
    Guru 24520 points

    Hi Evgeny,

    Thank you for your quick response.
    > What value does it show during normal operation?
    It showed about 46.2uH during normal operation.
    * We referred the sampled code of LDC1614EVM for our application code.

    > Can you reliably reproduce this phenomenon?
    Yes. We had a board which we could reproduce.

    I forgot to explain about background of this.

    We made the engineer sample board for detection the stress of metal plate on coil. And we made the three boards for sample. One of three, this phenomenon was occurred. And we had not met this phenomenon on CH1.  

    And it will be more likely to occur this phenomenon by putting the metal plate near coil on board.


    If you have any questions, please let me know.

    Best regards.

    Kaka

  • 0 in reply to Kaka
    Guru 24520 points
    Hi

    Would you please give us your comments for my response?

    Best regards.
    Kaka
  • 0 in reply to Kaka
    TI__Genius 9300 points
    Hi Kaka,

    Please check the amplitude of oscillations at INA pin. What is the capacitance value in your LC tank?
  • 0 in reply to Evgeny Fomin
    Guru 24520 points

    Hi Evggeny,

    Thank you for your response.
    I tried to capture the waveform of INA pin when this phenomenon was occurred.
    But, I could not captured it because it does not always happen.

    The typical amplitude of INA pin was 1.54V.
    And the capacitance in my LC tank is 1500pF.

    When I used the other coil board, it also happen the same issue.

     Inductance: 172uH
    Capacitance: 68pF
    Amplitude: 1.62V(typ)
    3.46V(max)

    If you need more information, please let me know.
    Best regards.
    Kaka

  • 0 in reply to Kaka
    Guru 24520 points
    Hi Evegeny,

    If I provide the schematics and layout date to you, would you please check them?

    Best regards.
    Kaka
  • 0 in reply to Kaka
    TI__Genius 9300 points
    Kaka-san,

    Yes, but please send them in pdf form.

    In the meanwhile, you mentioned 3.46V(max) - this is too high. How does it happen? A single spike to this amplitude, or somehow else? A screenshot would be extremely helpful.
    What reference frequency do you use?
  • 0 in reply to Evgeny Fomin
    Guru 24520 points
    Hi Evgeny,

    Thank you for your response.
    I would like to send you schematics and layout data. Would you please teach me your email address??

    Regarding to maximum voltage, it happen at the start of waveform. I captured this waveform and summarized it to pptx file. Also I would like to share with you in offline.

    The reference clock is 40Mhz. Just in case, I showed the URL of clock which I used for my board.
    KC3225A40.0000C3GE00: www.kyocera-crystal.jp/.../kc3225a_c3_e.pdf

    If you have any questions, please let me know.
    Best regards.
    Kaka