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ADS1256: RDATAC mode

Lucas Rosa
Prodigy 110 points

Part Number: ADS1256

Hi Team,

I have a question regarding the ADS1256 converter. I am currently reading my data in RDATAC mode, and I came across the information presented on page 22 of the datasheet, which reads:

"If there is a step change on the input signal while continuously converting, performing a synchronization operation to start a new conversion is recommended. Otherwise, the next data will represent a combination of the previous and current input signal and should therefore be discarded. Figure 21 shows an example of readback in this situation"

Can you please explain what this means? If my input signal changes abruptly while in RDATAC mode, do I need to SYNC the converter and wait for the settling time once more?

Thank you.

  • +1
    TI__Guru 59601 points

    Hi Lucas Rosa,

    A delta-sigma ADC samples the ADC input at a very high data rate, then basically averages this higher-speed data to reduce the noise and produce an ADC code that is output at a lower data rate

    Since the delta-sigma ADC is always sampling the analog input, you want to make sure your input signal is settled during the conversion process. If during the conversion process there is a step input, the ADC will average some data from before the step input and some data after the step input. This will yield erroneous data, or data that does not match the analog input.

    Therefore, if there is a step change you should restart the conversion process once the input has settled to avoid this issue

    Please see this app note for more information, specifically section 4: https://www.ti.com/lit/an/sbaa535/sbaa535.pdf?ts=1697067631205

    -Bryan