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LDC2112: Minimum Gap between Inductive sensing and PCBA’s IC

kaipeng chu
Intellectual 261 points
Part Number: LDC2112

Dear Sir,

 

I updated our product structure, please see attached JPG file.

We have two questions about the LDC2112 design that show as below, please help confirm.

1.The Minimum Gap between Inductive sensing and PCBA’s IC.

We have used ferrite sheet, what is the minimum distance between PCBA’s IC and sensor coil?

Are there related documents mentioning the conditions for our design? Can you provide a suggested distance.

2.How to choose the material and thickness of Ferrite?

Are there any relevant documents for reference? Or provide the recommended material.

B.R.

Ken

  • 0
    Intellectual 261 points

    Dear sir, 

    Update the questions, 

    We have 4 questions about the LDC2112 design that show as below, please help confirm.

    1.The Minimum Gap between ferrite sheet and PCBA’s IC.

    We have used ferrite sheet, what is the minimum distance between PCBA’s IC and sensor coil?

    2.The Minimum Gap between Inductive sensing and PCBA’s IC.

    We don't have used ferrite sheet, what is the minimum distance between PCBA’s IC and sensor coil?

    Are there related documents mentioning the conditions for our design? Can you provide a suggested distance.

    3.How to choose the material and thickness of Ferrite? also check the Permeability VS Frequency?

    Are there any relevant documents for reference? Or provide the recommended material.

    B.R.

    Ken

  • 0 in reply to kaipeng chu
    TI__Expert 7599 points

    Hello Ken,

    Thank you for your post. Our expert Engineer will get back to you very shortly on this. 

  • 0 in reply to Arjun_Prakash
    TI__Genius 17440 points

    Hi Ken,

    Questions 1 and 2 are primarily mechanical questions. I don't have an exact number to give you, but I can give you guidelines to think about:

    • The sensor coil should move as little as possible. FPC sensors should have a support structure and a stiffener to immobilize the sensor coil as much as possible, especially during button presses. The button response will be reduced if the sensor moves away from the coil during a button press, and this can lead to long-term reliability issues. From a mechanical standpoint, you only need enough space so that the sensor coil and its support structure will not touch the ICs, including manufacturing tolerances.

    • From an electrical standpoint, the sensor coil will be radiating an electromagnetic field at the sensor's resonant frequency. With the ferrite layer in between the ICs and the sensor, this radiation may not be an issue. I would not suggest placing sensitive ICs below the sensor without ferrite shielding. 

    For question 3, we have this blog post that discusses ferrite shielding. I suggest browsing through similar products to see what thicknesses are available that could work for your stackup. The permeability information will be available in the product's datasheet. 

    Finally, please note that you do need to have space for the metal target to deform, so the target cannot be touching the sensor coil. I realize that this may be a simplified drawing, but I just wanted to make it clear that there needs to be space between the target and coil.

    Best Regards,

  • 0 in reply to Kristin Jones93
    Intellectual 261 points

    Hi Kristin, 


    Yes, this is only a simplified drawing, we have noticed this space for the metal target to deform.

    About electromagnetic field, do you mean that the electromagnetic field generated by the sensor coil will affect the sensitive ICs  on the PCBA?

    Best Regards,

    Ken

  • 0 in reply to kaipeng chu
    Intellectual 261 points

    Hi Kristin, 

    About electromagnetic field, do you mean that the electromagnetic field generated by the sensor coil will affect the sensitive ICs  on the PCBA? or the sensor coil affected by other devices?

    Best Regards,

    Ken

  • 0 in reply to kaipeng chu
    TI__Genius 17440 points

    Hi Ken,

    It's more likely that the sensor coil's radiated field could impact the ICs. If they are not sensitive to the sensor frequency, then it may not be an issue, but it is safer to keep the ICs away from the coil.

    Unless the ICs are radiating a frequency within the narrow pass-band of the LC tank, they should not impact the sensor.

    Best Regards,