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FDC2214: how to select the LC tank values

Di Jiao
Intellectual 815 points
Part Number: FDC2214

Hi,

   I am using the FDC2214 for liquid level sensing and the input range is about 10nF to 200nF(the sensor contacts the water directly and the capacitor is large).

  TI suggests the typical choice is 18uH + 33pF.  I think this choice is for input range at several pF.

  1.  How to ensure the Vsensor is at 1.2V~1.8V? 

 2. For capacitor about several hundred nF. I want to select the origin LC tank as 47nH + 10nF. Is that more suitable for my application?

  Looking forward for your reply.

  Best regards,

  Di

 

  

  • 0
    TI__Genius 17440 points

    Hello Di,

    1. Please see this app note to ensure the drive current is set for the optimal sensor oscillation amplitude: http://www.ti.com/product/LDC1612/technicaldocuments

    2. These values will not work because the sensor Rp value will be too low for the FDC2214 to keep the LC tank oscillating. The FDC2214 requires a sensor Rp of at least 1kohm. The above app note discusses Rp further. In general, the LC values do not matter for resolution or sensing range; all that matters is that the FDC can drive the sensor. I suggest using the default values on the EVM and using the equations in the above app note to double-check that the sensor Rp value will be above 1kohm even at your highest input capacitance.

    Best Regards,