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FDC1004EVM, what is the meaning of C51 and C52

Shinichi Inoue
Guru 21686 points
Other Parts Discussed in Thread: FDC1004EVM, FDC1004

Dear Specialists,

My customer is considering FDC1004 and has a question about FDC1004EVM.

Could you please advise following ?

Question about FDC1004EVM. 

According to the schematic, the circuit is connected C51(51pF) to SHLD1 and C52(51pF) to SHLD2.

Is it needed?

What is the meaning?  

Best regards,

Shinichi

  • 0
    TI__Expert 7400 points

    Hi:

    Originally, the fixed capacitance on SHLD1 and SHLD2 were used to put some kind of load on the shield lines if they were not used. These are not required and can be left off.

    Thanks

    -David Wang

    Capacitive Sensing Applications

  • 0 in reply to David Wang11
    Guru 21686 points

    Dear David 

    Thank you for your reply.

    My understanding is listed below. Is it right?

    In the FDC1004EVM,

    SHLD1 is connected to left of the shield pattern.

    SHLD2 is connected to right of the shield pattern.

    But shield function is disabled by CS1 and CS2.

    Also could you please advise cap value.

    Why the capacitance value is 51pF?

    51pF is suitable in any cases?

    Best regards,

    Shinichi 

  • 0 in reply to Shinichi Inoue
    TI__Expert 7400 points

    You cannot disable the shield function.  The fixed capacitance are used when the shield Is NOT connected to anything, but as I mentioned, it is not required. If you really want to put a cap on it, any value will be sufficient.

    Thanks

    David Wang

    Capacitive Sensing Applications

  • 0 in reply to David Wang11
    Guru 21686 points
    Dear David

    Thank you for your reply.

    I understand the meaning of fixed capacitance.

    FDC1004EVM is connected to both shield and CS1(CS2).

    If the shield is connected , the CS may be connected .

    Best regards,
    Shinichi