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LDC0851EVM: The problem with hand-made inductor coils

Part Number: LDC0851EVM
Other Parts Discussed in Thread: LDCCOILEVM

Mr. John.
The voltage between LSENSE and LCOM of inductor coil, frequency and
I measured the voltage and frequency between LREF and LCOM.
Three different waveforms were measured between LSENSE and COM and between LREF and LCOM.
The frequency was C:80PF, L:23.67μH (one side), and I was expecting 3.7MHz.
The frequency was C:80PF and L:23.67μH (one side), which is more than one order of magnitude different from the expected 3.7MHz.

PHOTO1

PHOTO2

PHOTO3

From this phenomenon, it is conceivable that the two inductor coils
This phenomenon may mean that the two inductor coils are not connected correctly?

LSENSE coil on a universal board

LREF coil on the back side

That's all. Please let me know what you think.

Thank you for your cooperation.

  • Hiroaki,

    The images you uploaded are difficult to see the details.
    Would you please attach the image files to this thread?

    It is possible the wire-wound coils have different L and Rp than the design that was intended to be implemented on a PCB.
    Can you measure the inductance and Rp of your wire-wound coils, such as with an LCR meter?

    Also, the metal vias on your prototype PCB will certainly affect the coils' inductance and the impact of the target on your reference coil.
    Would it be possible to use a different PCB without any metal between your two coils?

    Regards,
    John

  • Mr. John.
    Thank you very much for your help.
    After the previous inquiry, I found a mistake in the wiring between the reference coil and the LDC0851EVM.
    After I found and corrected the mistake in the wiring between the reference coil and the LDC0851EVM, the frequency fsensor became 3.8Mhz~3.9Mhz, and the object can be detected.
    It is now possible to detect objects.

    I measured the R and L of the sensor side and the reference coil side, and the sensor side R: 120mΩ, L: 24μH, the reference coil side R: 118mΩ, L: 20μΩ, the L almost matches the design value, and the R is low.
    How do you feel about this?

    In addition, the metal vias used between the sensor coil and reference coil layers were used to simplify the prototyping.
    The metal vias used between the sensor coil and reference coil layers were used to simplify the prototyping, but would they be possible without a printed circuit board?

    I would like to incorporate it into the machine in the end, so please let me know if you have any examples of choosing something other than a printed circuit board.
    Please let me know if you have any examples of choosing something other than PCB.

    Thank you very much for your cooperation.


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

  • Hiroaki,

    I am glad you found the problem and that the design is working.
    The fact the design works means the vias are not an issue. 

    Unfortunately we do not have any examples of wire-wound coils. 
    Apologies for that.
    The applications we have seen emphasize a small space, and PCB coils were used.

    We have a EVM/PCB that provides examples of PCB coils, with a user's guide that gives electrical parameters of the various coils.
    You can see the LDCCOILEVM here and the user guide here

    Please let me know if you have any more questions.

    Regards