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FDC2214EVM: LC tank

Janine Lin
Expert 2190 points
Part Number: FDC2214EVM
Other Parts Discussed in Thread: FDC2214

Dear Kristin and Clancy

Here are my questions:

1. What is the purpose of LC tank in FDC2214?

2. Does increasing or lowering the value of  LC tank has a connection with the proximity sensing range?

Thank you!

Best Regards

Janine Lin

  • 0
    TI__Genius 17440 points

    Hello Janine,

    1. The LC tank is the fundamental part of the FDC2x1y devices. The FDC devices measure changes in the frequency of LC tank. When the sensor capacitance changes, the LC tank frequency will too. We have a blog post that should help explain how this is a different approach from traditional capacitive sensing.

    2. The sensor frequency itself is does not matter for the sensing range. I would not recommend selecting a large capacitor value, as this will make the system less sensitive to small changes in capacitance. Selecting a capacitor that is too small can make the system too sensitive to environmental or parasitic capacitances. The FDC2x1yEVMs use a 33pF sensor capacitor. I recommend using a sensor capacitor of similar value.

    Best Regards,

  • 0 in reply to Kristin Jones93
    Expert 2190 points

    Ok Kristin, I got it. Thank you~

  • 0 in reply to Kristin Jones93
    Expert 2190 points
    Hi Kristin,

    I have a follow up question. In datasheet it says the maximum input capacitance is 250nF. Is this the total value of C from LC and sensor electrode?
  • 0 in reply to Janine Lin
    TI__Genius 17440 points
    Hi Janine,

    This maximum capacitance value is only true for the LC tank inductance and frequency specified in the datasheet. The key parameters are the device's minimum and maximum sensor frequency and its maximum drive current. As long as you are not violating the sensor frequency limits and your sensor oscillation amplitude is between 1.2-1.8V, you can modify the inductance to accommodate most capacitances.

    Best Regards,
  • 0 in reply to Kristin Jones93
    Expert 2190 points
    Got it. Thanks Kristin.