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ADS1256: Electromagnetic interference

Lucas Rosa
Prodigy 100 points
Part Number: ADS1256

Tool/software:

Hi Team,

I have developed a board with the ADC mentioned. The ADC is about 8 cm from another board (same reference) in which a 5nF capacitor is discharged through a 3MΩ resistance. The voltage stored in this capacitor is 5kV. This system has been in production for about 1 year without any detected problems until now. The last boards produced are experiencing an issue related to the ADC.

The ADC is powered by a 5V regulator for its analog section and a 3.3V regulator for its digital section. When the discharge occurs, the 3.3V digital regulator (which has an internal limit of 100mA) drops to approximately 2V. The 5V analog section remains unaffected. I have found that the ADC is causing this issue. If I change the discharge resistance to 150MΩ (The discharge resistance must be <3MΩ), the problem does not occur. This issue has never happened before. Could you help me with this?

  • 0
    TI__Mastermind 40661 points

    Hi Lucas Rosa,

    Some questions for you:

    • Can you help us understand how you determined the ADC is causing this issue? It sounds like the discharge is causing this issue, which is negatively affecting the ADC and surrounding circuitry. Also, the ADC can work down to AVDD = 1.8V, so an LDO at 2V would not necessarily be an issue for the ADC
    • When you say the boards have the "same reference", does this mean that there is a voltage reference on one of the boards that is used for both (the ADC and maybe some other circuit)? Or is "reference" in this case referring to the ground i.e. the boards share the same ground reference?
    • How do you recover from this issue? Do you have to power cycle the boards? Or does the digital LDO return to 3.3V once the cap has finished discharging?
    • Is the cap discharging into the same ground as the ADC? Or do you have something like a PCB ground and an earth ground, where the ADC is connected to the PCB ground and the cap discharges to earth ground?
    • Can you provide a schematic of both boards?

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 100 points

    Hi Bryan,

    Yes, the ADC is affected by electromagnetic interference from the discharge. After the discharge, the ADC starts to warm up, and its 3.3V digital section supply goes to ~2V, causing both to get hotter.

    Regarding the same reference, I just wanted to clarify that the discharge's GND and the ADC's GND are the same. Both systems are powered by the same battery.

    Unfortunately, due to industrial confidentiality, I cannot provide the schematic unless we go offline.

  • 0 in reply to Lucas Rosa
    TI__Mastermind 40661 points

    Hi Lucas Rosa,

    You can share your schematic with me privately by requesting a friendship and then sending me a private message.

    -Bryan