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How to reduce Proximity & Frequency variation due to Temperature change

Ronny Vrijelinck
Prodigy 50 points
Other Parts Discussed in Thread: LDC1612, LDC1612EVM

We see that the Proximity value and the Measured Sensor Frequency is very sensitive to Sudden Temperature change and that its takes a very long time(+30min) before the measured values stabilize after a sudden Ambient Temperature change of for example +/-45°C (15°C to 60°C) see also below Graphs

Can we do something in our circuitery so that this behaviour is compensated?

  • 0
    TI__Expert 6550 points
    Hello Ronny,

    Could you please tell me the characteristics of the capacitor and the coil you are using?

    Please take a look at the following app note on temperature compensation: http://www.ti.com/analog/docs/litabsmultiplefilelist.tsp?literatureNumber=snaa212&docCategoryId=1&docCategoryId=9&familyId=82&keyMatch=ldc1000 temperature compensation&tisearch=Search-EN

    Best Regards,
    Natallia Holubeva
  • 0 in reply to Natallia Holubeva1
    Prodigy 50 points

    Hello Natalia,

     The coil we use is a coil with a ferrite core and it has a value of 680µH and a serial resistance of 2.1 Ohm

     We tested with 2 different Caps

     1. a cap of 15nF Giving a resonance Freq of approx 47KHz, in this situation we see a very big anomaly in the measured values only stabilizing after approx 30minutes

     2. a cap of 100pF giving a resonance of 345KHz, in this case the anomaly is much smaller but we see still a stabilization drift over approx 30minutes

     In the app note describes actions that can be done on the coil , but in my opinion the anamoly and the stabilization drift is in our case mainly caused by the

     electronics inside the LDC.

     What can be done to solve this?

     Kind regards

     Ronny

  • 0 in reply to Ronny Vrijelinck
    TI__Expert 6550 points

    Hello Rony,

    Thank you for explanation. Besides the coil design, there is not much you or I can do inside of the IC. Taking a differential measurement of two coils and performing temperature compensation in software is the most common way to approch the problem.

    Could you please check the capacitance of the cap before and after the temperature drift? What is the temperature coefficient of the cap you are using?

    L-measurements are far superior in terms of temperature stability. If L alone isn’t good enough, then you could also use two identical coils (one with moving target for proximity measurement, and one without target for temperature compensation). The LDC1612 accomplishes this beautifully.
     
    Best Regards,
    Natallia Holubeva

  • 0 in reply to Natallia Holubeva1
    Prodigy 50 points

    Hello Natallia,

     Thanks for the support,

     We will check the possibility of using the LDC1612 and other possibilities to solve the issue.

    Kind  Regards

     Ronny

  • 0 in reply to Ronny Vrijelinck
    Prodigy 50 points
    Hello Natallia,

    The LDC1612EVM and the LDC1612 chip doesn't seem to be available , not at the distributors or the TI Store
    How can i aquire a LDC1612EVM to evaluate the LDC1612 and check if it's suitable for our application?

    Kind Regards
    Ronny
  • 0 in reply to Ronny Vrijelinck
    TI__Expert 6550 points
    Hello Ronny,

    LDC1612 was released this week. Usually it takes few days until you can order it. By any chance, did you check the capacitor you are using? Also, could you please help me understand on what conditions the temperature is changing?

    Best Regards,
    Natallia Holubeva