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Touch Coil samples does not work in our desgin with IT design guide

Other Parts Discussed in Thread: LDC2114

Hello, TI engineer

This is Zhanhang Fang from GREE in Zhuhai City.

LDC2114 sample we used in project. Coils sample we designed by ourselves.

In our main board + TI touch coil sample , they can work. But our main board + our touch coil sample, did not work.

Parameters are below, and Q value is correct. 

How can we konw what were the problems ?    How can we check ? 

Thanks for your help .

  • Hello,

    Unfortunately your images did not come through. Can you reattach them?

    In general, there are two good ways to check the coils. The first is to measure the inductance the Rp value across frequency. Instructions for measuring the Rp value can be found here. Once you have the measured values, make sure the Rp value is within the design space of the LDC2114. Then calculate the fsensor and Q value of your sensor and verify that these are in the LDC2114's design space as well. The formulas and design spaces are listed on pages 29-30 of the datasheet.

    The next step is to probe the sensor oscillation with an oscilloscope. For the LDC2114, we recommend isolating the oscilloscope probe from the sensor with a ~1k resistor. This prevents the probe's capacitance from loading the LC tank sensor and shifting the measured resonant frequency. Ensure that the sensor is oscillating at the correct frequency (calculated above) and at a normal amplitude. For more information about probing the LDC2114 sensors, please see this e2e post.

    Best Regards,

  • Hello  Jones,

    Thanks for your adviseing and link.

    Our coil parameter as below, show again.

    PCB coil was made as  the parameter.  Our coil + our main borad ,they can work, but the sensing distanace was short, less then 1mm.

    The inductance value I test was 0.11uH. There should be something wrong.  Is there anything wrong in parameter I input ?

    In my mind, the shorter of the spacing( 4mil ) and width ( 4mil ), the larger of the inductance value.  

  • Hello Jones

    image as below.

  • Hello,

    Can you clarify how you measured the coil's inductance? I don't see a problem with your inputs in the Spiral Inductor Designer.

    Also, is your sensor capacitor on the main board?

    Best Regards,

  • Hello,

    I haven't heard from you in a while, so I'm assuming you were able to resolve your issue. If this is not the case please feel free to reply to this thread or post a new question.

    Best Regards,