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ADS7828: Device latch in error state

Mark McGahan
Prodigy 190 points
Part Number: ADS7828


Sometimes the AD7828 appears to latch up in a state where the digital output for all channels does not match the apparent input. For example, a channel connected to an RTD has an input voltage corresponding to a temperature in the range of 19 - 25 degrees C (which corresponds to the actual temperature in the system), but the digital output for that channel corresponds to temperature of  -80 degrees C. This state persists until the system is power-cycled.

  • 0
    TI__Mastermind 25030 points

    Hello Mark,

    This is odd behavior. I will need a some background information to further debug this.

    What is the state of the input and the ADC before the latch up occurs? Has the input been measured with a multimeter to confirm that voltage is correct?

    Is there any glitches/dips in the power supply?

    Does this occur with every channel or just one channel? when the latch up occurs, no matter what the input is on any channel, the device continues to send incorrect SDO data?

    Regards

    Cynthia

  • 0 in reply to Cynthia
    Prodigy 190 points

    Cynthia,

    Thanks for your reply.

    Regarding your questions --

    1. What is the state of the input and the ADC before the latch up occurs? Has the input been measured with a multimeter to confirm that voltage is correct?

    So far we have only seen this problem very infrequently while the PCB with the ADCs is inside a unit with very limited access. So we have not been able to verify the voltage on the ADC analog inputs.

    2. Is there any glitches/dips in the power supply?

    Not that I know of. I will run more tests and provide more information when possible.

    3. Does this occur with every channel or just one channel? when the latch up occurs, no matter what the input is on any channel, the device continues to send incorrect SDO data?

    We have seen at least one case where every channel is impacted.

    Please be aware that my company has instituted a work from home policy due to Coronavirus concerns, so I will have very limited opportunities to pursue this further in the next several weeks.

  • 0 in reply to Mark McGahan
    TI__Mastermind 25030 points

    Mark,

    I understand, when you are able to continue to work on this and further debug please reach out again

    Regards

    Cynthia