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WEBENCH® Tools/LDC1614: PCB coil fill ratio

Part Number: LDC1614

Tool/software: WEBENCH® Design Tools

Dear TI

Here are my questions.

1. What is the relation between PCB coil fill ratio and Q factor. What are their differences? 

2. In designing a coil, what this temperature for? 

3. What is voltage (oscillation amplitude)? 

Thank you

  • Hi Janine,

    1. The PCB coil fill ratio is the inner diameter of the coil divided by the outer diameter of the coil. It's a way to measure how much of the center of the coil is left open. Typically, the inner turns do not offer significant increases in inductance or sensitivity, but they do increase the Rs (and therefore decrease Rp). It's desirable to keep Rp high, so we recommend keeping a coil fill ratio of at least 0.3.

    The LC tank is inherently a narrow band-pass filter, and the Q factor represents how narrow or broad the passband is. A higher-Q filter will be more resistant to noise. Q is affected by Rp, L, and C (see equation 2 in the LDC1614 datasheet). Keeping the coil fill ratio within the recommended guidelines will optimize Rp and L, which will in turn optimize Q.

    2. Rp (and therefore Q) change significantly with temperature, so the temperature input can be used to check if your coil design meets the Rp specification in the datasheet across your expected temperature change.

    3. The LDC1614's SNR is optimized when the LC tank's oscillation amplitude is between 1.2-1.8V. You can specify a target sensor oscillation amplitude and the Webench tool will output a recommended drive current and estimated power dissipation.

    Best Regards,
  • Thank you Kristin.