This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LDC2112: LDC2112 resonant frequency measure and -2048 mean

Part Number: LDC2112

Hi:

1. Could we use oscilloscope probe measure INn capacitor pin to see the resonant frequency?

   Since we want to know if the resonant frequency is as what we design

   And if can't, what way can we measure resonant frequency?

2. If the raw data value always show -2048, do you know what it mean? 

Thank you~~

Poki

  • Poki,

    Thank you for your inquiry and your interest in TI products.

    1. You can probe the INn capacitor with an oscilloscope, but even the small probe capacitance may shift the resonant waveform away from the desired frequency.
    2. What is the circuit, sensor and target configurations that results in the 2048 raw data value?

  • Hi John:

    Thanks feedback

    1.So if oscilloscope probe will have big error, any way that we can measurement resonant frequency?

    2. it's -2048 (negative 2048), I know it's abnormal. Below chart is our device, our sensing coil is on FPC, and the situation is, when we not assembly the FPC (left one), the value is normal (close to 0), but when we assembly the FPC(the middle one),  the value will become -2048, so I want to ask some questions

       a. The FPC neck area bending larger at assembly, will it cause -2048?

       b. At assembly, if FPC larger bending cause the FPC golden finger connection not good with zip connector, will it cause -2048?

       c. Or do you think anything that could cause -2048?

    Thank you~~

    Poki

  • Poki,

    It sounds like your device is saturating for one of your configurations, resulting in the -2048 value.

    Would it be possible to give some more details about your application?

    I am not sure what you meant in your reply 2/b.

  • Hi John:

    Sorry I forgot attached chart, please see below chart

    When not assembly(the left one), the value is normal(~0), and when assembly(the middle one), the value become -2048

    But we have some finding, that if we assembly then reboot system, the value become normal

    Is that mean at initial the LDC2112 will do calibration for present configuration, so if configuration change, we need do another initial or the value will become abnormal?

    And if we dump those two configuration register when doing initial we will see different setting?

    Thank you~~

    Poki

  • Hello Poki, 

    It seems like the change in the coil is causing the data to go to a max negative. If rebooting the system works, then it is a problem with the large mechanical change during the assembly. If you do not want to reboot the system, you can also reset the LDC2112 measurement baseline by entering and then exiting config mode. You may also want to check out the LDC2112, LDC2114 Internal Algorithms Functionality app note which has information on the baseline tracking and the different ways that it can be reset. 

    Best Regards,