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ADS131M06: Accuracy of internal test signals

Nicolas Verbeek
Prodigy 40 points
Part Number: ADS131M06


Hello,

For testing the ADS131M06 ADC I am using the internal test signals. According to the datasheet, they should be at 2/15*Vref, which is 160mV nominal under unitary gain. I'm using the internal voltage reference of 1.2V nominal. When measured using the ADC, I obtain values between 0.1524V and 0.1528V for the different channels. Similar values are obtained when using the negative test signals. Both the precision between channels and for a single channel over time seem fine. However, the accuracy seems way off by almost 5% compared to the nominal value of 160mV. Neither the gain error of the ADC, nor the accuracy of the internal voltage reference can explain this. Is this expected behavior? What is the accuracy of these internal test signals?

Thank you very much in advance.

Best regards,

Nicolas Verbeek

  • 0
    TI__Mastermind 46115 points

    Hi Nicolas,

    Thank you for your query on the forum, I'm checking now and will get back to you soon.

    Regards,

    Dale

  • +1 in reply to Dale Li
    TI__Mastermind 46115 points

    Hi Nicolas,

    When the internal 1.2V voltage reference is used, the signal is scaled down, so the right voltage you should get is 160mV*(1.2V/1.25V) = 153.6mV. When an external 1.25V voltage reference is used, you should be able to see the test signal around 160mV. We will try to make the datasheet clear in the future. Thanks.

    Regards,

    Dale

  • 0 in reply to Dale Li
    Prodigy 40 points

    Hello Dale,

    Thank you for your answer. This clears things up.

    However, I obtain ADC values between 152.4-152.8mV while the reference should be at 153.6mV: the error is still larger than the accuracy of the internal voltage source (0.1%) + ADC gain and offset errors. Would you happen to know the accuracy on the divider ratio for obtaining the 153.6mV ?

    Best regards,

    Nicolas Verbeek

  • 0 in reply to Nicolas Verbeek
    TI__Mastermind 46115 points

    Hi Nicolas,

    This internal test signal is only used to test the device's functionality, not for performance verification. Also, I already checked with the team, we do not have a data for the accuracy of the test signal.

    Best regards,

    Dale