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LDC0851: About the LDC core of LDC0851

HIROAKI YOSHIDA
Intellectual 290 points
Part Number: LDC0851

Thank you very much for your help.

I am considering a proximity sensor using LDC0851, and would like to know the following: LDC0851 is used in threshold mode with stacked coil.

Question 1: The "Differential LDC Core" shown in the internal block diagram of the LDC0851 is an oscillation circuit, and I imagine that it is an oscillation circuit in which the oscillation amplitude changes depending on the feedback current.

Question 2: The comparator between LSENSE and LREF compares the oscillation amplitude and the threshold value, but does this compare the feedback current?

Please tell me about "Differential LDC Core" in as much detail as possible.

  • 0
    TI__Mastermind 33250 points

    Hiroaki,
    As you mentioned, the sensors act as oscillators where the frequency varies as a function of the target position.
    For all of our LDC devices, the digital core is counting the axis crossings of the sensors/oscillators over a measurement interval.
    The LDC081 data sheet gives this time as  t_conversion. 

    The device uses the number of axis crossings to estimate the sensor frequency, which in turn allows an estimate of the inductance. 
    There is a reference clock that runs at a much higher frequency than the sensor and it serves as a reference for counting the axis crossings, and also oversampling of the overall sensor waveform. The oversampling is what allows these devices to provide enhances resolution. 

    Would you please clarify what is meant by feedback current?
    This device functions as a comparator, so I am not sure how feedback would affect its operation.

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Intellectual 290 points

    Mr. John.

    Thank you very much for your help.
    Could you tell me more about LREF and LSENSE?
    According to the LDC Differential Inductive Switching/Data Sheet Figure 1, it looks like the LREF (reference coil) is the active coil and the LSENSE (sensor coil) is the passive coil.　
    Or is it possible that both LREF and LSENSE are active coils and operate as passive coils for eddy current/magnetic field inductance change, although it is not shown in the timing chart?
    Or are LREF and LSENSE both active coils and passive coils for eddy current/magnetic field inductance change?

    Thank you very much for your help.

    Hiroaki Yoshida


    Translated with www.DeepL.com/Translator (free version)

  • 0 in reply to HIROAKI YOSHIDA
    TI__Mastermind 33250 points

    Hiroaki,

    Both coils are driven with signals. In that sense they are both active.
    Only the LSENSE is intended to have its inductance changed by the target.
    The LEF inductance is intended to stay constant.

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Intellectual 290 points

    Mr. John.

    Thank you very much for your help.
    Could you tell me a little more about the internal workings of the LDC0851?
    The two LDC cores are
    The LSENSE side calculates the inductance from the feedback current detected by the oscillation circuit and the detector circuit, adds the offset by ADJ, and outputs it to the comparator with schmitt.
    The LREF side outputs the oscillation circuit and reference inductance to the comparator.
    The level discrimination by the comparator becomes the object detection output.
    I think that's all.

    Please let me know if I am mistaken or if there is anything important that I missed.

    Hiroaki Yoshida

    Translated with www.DeepL.com/Translator (free version)

  • 0 in reply to HIROAKI YOSHIDA
    TI__Mastermind 33250 points

    Hiroaki,

    You are correct. That is how the device works.

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Intellectual 290 points

    Mr. John.

    Thank you very much for your help.
    Thanks to you, I understand a little more about LDC0851.

    Also, could you please tell me about the sensor coil?
    In the LDC sensor design, there is no mention of an "iron core" in the inductor coil design, although there is a picture of what appears to be an "iron core" in Figures 2.17 ~ 2.19. Should I assume that an "iron core" is not generally used in LDC systems?

    I would like to use the calculation results for the inductor coil as support for the inductor coil, so please explain the case where an "iron core" is used.

    Hiroaki Yoshida

  • 0 in reply to HIROAKI YOSHIDA
    TI__Expert 7589 points

    Hi Yoshida-san,

    Thanks for your interest on LDC0851 parts.... As your recent post is in regards to a coil design please post it as a new question by clicking on the "Ask a related Question" We would like the community to benefit from questions and answers so I appreciate in advance your efforts here. For now I will close this thread. Thanks.