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LDC1614: Sensor coil inductance (installed in system)

K.Yaita
Guru 29710 points
Part Number: LDC1614
Other Parts Discussed in Thread: TIDA-01102

Hi Team,

TIDA-01102 shows the following Table 5.
http://www.ti.com/lit/ug/tiducr1/tiducr1.pdf



1)
I believe "Sensor coil inductance (free space)" can be estimated by Webench Coil Designer.
Is my understanding coorect?

2)
Is "Sensor coil inductance (installed in system)" the value which is just measured value after installed?
Is it possible to estimate it before design?

Best Regards,
Yaita

  • 0
    TI__Genius 13335 points

    Hello,

    Your understanding on both points is correct. Estimating the exact inductance before building and measuring can be difficult. However, you can get a very coarse estimation using the Spiral Inductor Designer tab on the LDC tools spreadsheet: http://www.ti.com/lit/zip/slyc137 

    Entering the parameters above predicts a free space coil inductance of about 20.87µH which is very close to the measured 21µH. Then entering the Target Distance as 0.4mm drops the inductance to about 5.69µH which is a bit off from the measured 8µH but still in the ballpark as a very coarse estimate. The reason is the calculator assumes an aluminum target which is more conductive than stainless steel so it provides more inductance shift. You can see this effect in the target design application note from figure 12: http://www.ti.com/lit/pdf/SNOA957

    Regards,

    Luke

  • 0 in reply to Luke LaPointe
    Guru 29710 points

    Hi Luke-san,

    Thank you for your kind support.
    I would like to ask an additional question.

    >The reason is the calculator assumes an aluminum target which is more conductive than stainless steel so it provides more inductance shift.
    What is the size of target that the calculator assumes? Is it same with coil size (dOUT, dL)?

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    TI__Genius 13335 points

    Hello Yaita-san,

    The tool assumes that the target covers >100% of the coil diameter. If the target covers less than 100% of the coil, then the response will decrease. We have written a blog article discussing how target coverage effects the response of the LDC: e2e.ti.com/.../inductive-sensing-target-size-matters

    Regards,

    Luke