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Use of SHLD pin in FDC1004

AMAN MAHAJAN
Prodigy 10 points
Other Parts Discussed in Thread: FDC1004

Hey 

as per FDC1004 datasheet SHLD is use to avoid parasitic  capacitance ?

so i want to know how it protect against parasitic capacitance n can we connect this pin with some external capacitance say 0.1uF ?

thank you

aman mahajan 

  • 0
    TI__Expert 7400 points

    Hi Aman:

    Yes the shield is used to help reduce the amount of parasitic capacitance from the surrounding areas to affect the measurements. The SHLD is exactly the same waveform and potential as the driving signal to the CIN electrode. This allows pairing between them. No direct coupling with occur between them because they are the same potential (no difference thus no capacitance). The shield will be used to couple to any external parasitic capacitance and reduce the effects to the actual capacitance measurements.

    Usually, on a PCB, you would have a shield layer directly underneath the CIN layer (electrode) so that any interference from the bottom or the sides will be reduce. There is no reason to connect external capacitance to the shield because that would affect the total capacitance load. Our shield drivers are only capability of driving up to 400pF of capacitance load.

    Please see the app note "The Ins and Outs of Active Shielding". That will have more information about the shielding and how to use it properly.

    Thanks

    -David Wang

    Capacitive Sensing Applications