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LDC1000: how to increase precision

Other Parts Discussed in Thread: LDC1000EVM

Hello,

we are using LDC1000 on a project where the PCB coil is the same of the LDC1000EVM (we used the Texas gerber file). All of the components of the circuit are the same of the EVM. The only difference is that in our sensor VDD = VIO = (short circuited) 5V.

Ctank is also the same of the LDC1000EVM, so we have a resonance frequency of approx. 3.6MHz. We need to reduce this frequency due to  increase our ODR range to reach better precision, defined as:

 

                                               DELTA ODR temperature

precision        =       ----------------------------------------
                                   DELTA ODR calibration range

 

 

Since we can not change the L value, we can only change the Ctank value.

We tried on the LDC1000EVM incresing the Ctank up to 35nF (200kHz resonance frequency). Over this value the LDC circuit does not working.

On our application we can't go over 500pF.

Why this difference? Maybe the VDD = VIO can cause this differnce?  Have you any suggestion? How to maximize ODR range without to modify the target position?

 

Best regards

 

  • Hello,

    With increased cap value Rp value goes down, and eventually violates DS spec of 800Ω.

    If you cannot increase the footprint of a coil, here's a few ideas how to make it work:

    Your major challenge is Rp = L/Rs/C.

    Easiest way to increase it is to increase L. For a given footprint you can increase inductance by adding more layers, or using smaller trace width/spacing.

    Then you could work on Rs - series resistance of the coil. You could decrease it by using 3oz copper for your traces.

    And last, but not least, you could try wound unshielded power inductors which will have much higher inductance.