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Original question:

LDC2114: LDC2114 Layout Example

LDC2112: LDC2112 transmission line INn shielding

Poki Huang
Expert 1080 points
Part Number: LDC2112
Other Parts Discussed in Thread: LDC2114,

Hi


According snoa961 page 17, INn need shielding top and bottom with COM


Could we shielding only top or bottom with COM?


I see topic "LDC2114: LDC2114 Layout Example" and your feedback is ok if INn is on PCB as below


"The recommended layout in the LDC211x Datasheet shows the INx traces on the top layer with COM shielding underneath but without COM shielding above. For applications where it is not possible to physically touch the INx trace, this design can be acceptable. If the sensor is not integrated into the PCB, then the use of shielding on both top and bottom is recommended"

We teardown fitbit charge 3  (you can ref.  www.techinsights.com/.../1652) , we think it's FPC is for inductive touch coil and the FPC is 2L


Since our product is wearable the same with fitbit, can we use only one layer to shield INn?

If yes, we should use top not bottom layer as shielding to avoid outside inferference right?

Thank you~~

BR/Poki 

  • 0
    TI__Genius 17440 points

    Hi Poki,

    Unfortunately I can't comment on the Fitbit teardown.

    We do recommend that you shield the top and bottom of the INx trace with COM. If it is not possible for you to use more than 2 layers in the FPC, it may be acceptable to only shield one side of the FPC. However, it may be more susceptible to parasitic capacitances.

    Best Regards,

  • 0 in reply to Kristin Jones93
    Expert 1080 points

    Hi Kristin:

    By topic "LDC2114: LDC2114 Layout Example" as below

    "The recommended layout in the LDC211x Datasheet shows the INx traces on the top layer with COM shielding underneath but without COM shielding above. For applications where it is not possible to physically touch the INx trace, this design can be acceptable.

    So could you explain more clear what status we can shield INx only one side?

    Thank you~~

    BR/Poki

  • 0 in reply to Poki Huang
    TI__Genius 17440 points

    Hi Poki,

    My apologies for the delayed reply. As long as the INx trace is fully enclosed by the mechanical structure it should be okay to only shield one side. An application that has an exposed cable between the sensor and the LDC2112 would need shielding on both sides, because it would be exposed to parasitic capacitances (such as a user touching the cable) that could impact the measurements.

    Best Regards,