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ADS1255: the interference in input

Part Number: ADS1255

Hi team,

My customer is evaluating ADS1255 in their project and met below issue now, could you please help review and give some suggestions? Thank you.

1. When using the ADS1255, the ADC input can be disturbed by the crystal.

2. The input port waveform has 1.92MHz interference, the crystal is 7.68Mhz

3. The input signal waveform 

4. Crystal Waveform 

5. Schematic. The1.92Mhz interference is introduced in input that disappears when the ADC is not working.

6. PCB

Regards,

Ivy

  • Hi Ivy Jin,

    Can you please post the customer name in the e2e post notes. This is only visible by TI, and it will be helpful for tracking purposes

    Regarding the issue: you posted two scope shots called "The input port waveform has 1.92MHz interference, the crystal is 7.68Mhz" and "The input signal waveform " - what is the difference between these images? Maybe a better question is where in the schematic are these measurements taken? Is the "input signal" before the INA and the "the input port waveform" is where the arrow is pointing on the schematic?

    The1.92Mhz interference is introduced in input that disappears when the ADC is not working.

    Can you explain in more detail what this means? Do you mean that when the ADC is not powered, there is no interference signal? In other words, the interference signal can be measured on AIN0 when the ADC is powered, but when you turn the ADC off, the interference signal goes away and the INA output is correct?

    Thanks for sending the PCB layout, I don't like the split planes running underneath the ADC. This can cause all kinds of emissions when the ground currents are disturbed. If the customer can change the layout, I would definitely make sure there is a solid ground plane.

    Let me know the answers to my questions and we can continue trying to troubleshoot this issue

    -Bryan