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ADS1256: +/- 640 offset error counts in OFC register

Jacco Dekkers
Prodigy 30 points

Part Number: ADS1256

We are experiencing strange problems with the ADS1256 ADC. We use self calibration to get the best value we can get since we are looking to very small amounts of counts.

In time, we see a steady number of let us say 550 counts in the OFC register. Sometimes there are offsets to be seen in this steady signal and they are 640 counts in number. So, sometimes we see 550 + 640 = 1190 counts in the OFC data and sometimes we see 550 - 640 = -90 counts. A sort of tri-state, so to speak.

We have tried different timings but so far the "glitches" are there to stay. Is there something wrong inside the ADC IC?

Regards,
Jacco Dekkers

  • 0
    TI__Guru 59161 points

    Hi Jacco,

    Are you performing an offset calibration before each measurement? Or are you only performing the calibration periodically?

    Do you change the ADC settings (data rate, gain, buffer configuration, etc.) during the calibration process?

    If you can provide any more details about how your specific calibration procedure and anything out of the ordinary that occurs during the "glitches", that would be helpful.

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 30 points

    Hi Bryan,

    The calibration is done each time we change of PGA setting and worst case that is after each measurement. All other setting stay the same, 100 SPS and Buffer On.

    But also a non changing set-up with calibration each time can have the irregularities, see following picture.

    Regards,
    Jacco

  • 0 in reply to Jacco Dekkers
    TI__Guru 59161 points

    Hi Jacco,

    Can you send me the raw codes you are reading from the OFC registers, as well as the conditions used for these values (gain, data rate, buffer)? From your description it seems like this issue can occur without changing any settings, so if you can just keep one set of conditions that would be helpful to eliminate as many variables as possible.

    Thanks!

    -Bryan