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LDC0851EVM: Designing with EVM and LDC_Too;s-ext49.xlsx

Part Number: LDC0851EVM
Other Parts Discussed in Thread: LDC0851

Hello, I'm looking at using the LDC0851 to detect the presence of a .090" thick cold rolled steel plate.  I have the LDC0851EVM to prototype with and it works pretty well.  I have a couple of questions about coil design.

I found the LDC_Tools-ext49.xlsx and it has proved to be pretty useful, thanks for that!  But when I plug the numbers from the LDC0851EVM documentation for coil diameter, 2 layers, 6 mil trace and space, 1 oz copper for a circular coil I don't get the 6.2uHy inductance that the EVM states for the coil on it even with cranking down the spacing between the layers.

Also, when designing the coil using the Spiral Inductor Designer spreadsheet with the 0851 chosen and then plugging the numbers from that into the LDC0851_calc spreadsheet, I get different results for sensor frequency and inductance with target.  Which spreadsheet should I trust more?

One more question.  In my design the plate will be on the sensor.  The design will alert the system if the plate is off the sensor.  Do I use the Ind/Freq chart to determine the best operating point?

  • Hi Domenic,
    We've got your request and we will get back to you soon.

    Best Regards,
    Bala Ravi
  • Domenic,

    As long as you have the LDC0851 selected on the spiral inductor designer tab, you should get the correct frequency measurement. The spiral inductor designer is probably using a better estimate than the LDC0851 for the frequency/inductance with target interaction.

    You are correct that the inductance/frequency plot is there to show you the allowed design space.

    Please note that the spiral inductor designer is an estimate, and it can be off. You always need to check the final inductance values of the coil. Most likely, the documented inductance of the coil was measured using an impedance analyzer.