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Reducing bus/power noise noise with FDC1004

Erik Strand
Prodigy 10 points
Other Parts Discussed in Thread: FDC1004, LP2985, LP5907

Hello,

I've been testing the FDC1004 for use in a proximity sensor. Using the evaluation board and sampling at 100hz, I typically get a standard deviation of about half a fF. When I use an Arduino to read values from the FDC1004 over I2C, however, I typically get larger values. The noise seems to depend heavily on the bus noise and/or power supply. Do you have any suggestions on how to mitigate these issues? I'd like to match the performance of the evaluation board.

To provide some concrete examples, when powering the Arduino (and FDC1004) over USB bus power and running off of my laptop's batteries, I can get a standard deviation of just over 1fF, but if I plug the laptop in it jumps up to around 12fF (and the noise then varies periodically at about 0.5Hz). On another computer, whether it's plugged in or not I can't get a lower standard deviation than 3fF, and when I ran the Arduino off of an external regulated power supply it actually made the standard deviation jump to 6fF.

Thanks,

Erik

  • 0
    TI__Expert 7400 points
    Hi Erik:

    I am not sure what kind of filtering is done on the Arduino board, but typically, we have been using LDOs to help filter out the bus noise. Most of the EVMs and reference designs either have the LP2985 or the LP5907, both have very good PSRR. We are in the process of doing PSRR tests with the FDC1004 to see what kind of performance it has.

    Thanks
    -David Wang
    Capacitive Sensing Applications