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LDC1612 Coil Design and Calibration

Huichen Zhang
Prodigy 80 points
Other Parts Discussed in Thread: LDC1612

Hey!

I am designing PCB coils for LDC1612. The WEBENCH tool gives me the capacitor value of 24.9pF. And the BOM list gives me a capacitor with value of 22pF. May I know if this is critical?

At the same time, I am using axial sensing technique for distance sensing. Do I need to calibrate the sensor with micrometer or some other tools before actual application?

And last question is, is there a way to properly mount the PCB coil and the metal target? To avoid interference, I guess I cant use screws to mount them. So do people usually mount the PCB coil and metal target with glue?  Is there a way to properly align the PCB coil axis with the round metal target central axis?

Thank you!

  • 0
    TI__Genius 13335 points

    Hello Huichen,

    The value of capacitor affects the oscillation frequency by the equation fsensor = 1/(2π*√(L*C) ).

    For more information on the fundamentals of LDC operation and sensor design please review the following application note: LDC Sensor Design (http://www.ti.com/lit/pdf/snoa930)

    Note that changing the frequency slightly with component selection has a minimal effect on the sensor frequency and overall operation. However, selecting a very small value such as 22pF may not be the best choice, because there are also parasitic capacitances on the board and in the environment. You will want the dominant capacitor in your system to be the capacitor you select for the LC tank. The dielectric should be NP0/C0G because it provides a very stable oscillation and has a low temperature coefficient.

    Your question about calibration depends on the specific application. Most applications do not require calibration because you are looking for a relative frequency measurement. The LDC1612 will report the frequency change in your system due to metal movements. You will need to correlate this to distance for axial sensing. And depending on the accuracy required you may need an additional sensor for mechanical tolerance compensation.

    With regards to mounting techniques it again depends on the application. For Metal Touch buttons, we typically use a double sided adhesive and compress the metal + spacer + coils together. 3M makes some good PSA materials for this purpose. For more information please see the following application note: Inductive Sensing Touch-On-Metal Buttons Design Guide (www.ti.com/.../snoa951)

    Please let us know if this answers all of your questions.

    Thanks!
    Luke LaPointe