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ADS8332: Analog input signal would be interfered when communicating with SPI

Garrick Dai
Intellectual 1660 points
Part Number: ADS8332

Hi Team,

My cusotmer is using ADS8332 and found the INx input signal will be interfered when MCU communcate with ADS8332 by SPI. If no communcation, then INx become normal and clear. So it seems SPI(digital cirucit ) will impact analog input circuit. Already checked customer circuit and layout design, analog ground and digital ground separated and follow design guide. Customer need to know why and how to avoid this? Please check. Thanks.

Below left is INx input signal when SPI not working, while right pic is INx input signal when SPI working.

   

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    TI__Mastermind 36150 points
    Hi Garrick,

    Unfortunately, the pictures did not make it through. Can you try reposting? This is likely a board layout issue, but could be a very subtle path where digital edges are coupling into the analog inputs.

    One way to help with digital coupling is to add 50ohm resistors in series with each of the digital lines. These will work with the pin input capacitance to create a low pass filter, reducing the total noise.

    Regards,
    Keith N.
    Precision Data Converters