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ADS114S08B: How could ADS114S08B behave in ext.VREF < 0.5V?

Iwata Etsuji
Expert 6400 points
Part Number: ADS114S08B
Other Parts Discussed in Thread: ADS114S08

Hi team,

According to "Comparing the ADS114S06 and ADS114S08 Standard and Cost-Optimized (B-Grade) ADCs", ADS114S08B doesn't have the Reference Detection.
Therefore, when the VREF drops below 0.5V, how could ADS114S08B behave?
i.e. What code could be generated in VREF < 0.5V? it keeps 7FFFh, 8000h, 0000h, or undetermine?

Best regards,
Iwata Etsuji

  • 0
    TI__Guru** 113765 points

    Hi Iwata-san,

    The VREF input voltage specification is for performance over the supply range and temperature range of the ADS114S08B.  Initially you will start to see linearization error.  The output code will also be dependent on the input voltage. So accuracy will be degraded, and the output code may or may not be representative of what is happening at the input.  So the output code is best defined as undetermined.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    TI__Expert 6400 points

    Hi Bob-san,

    Thank you for your support.

    I understood the difficulty to know what is happening at the input.
    However, we need to know the validity of the VREF input for ADS114S08B.
    How could we detect VREF loss in the case of ADS114S08B?

    Furthermore, if you had done FMEA apploach for it, it might be appreciated, such as output code in VREF=0V...

    Best regards,
    Iwata Etsuji

  • 0 in reply to Iwata Etsuji
    TI__Mastermind 23975 points

    Hi Iwata-san,

    I assume you are asking those questions because you want to detect an open wire in an RTD measurement application, is this correct?
    We have a few ways to detect that.

    If you use the REFP1/REFN1 reference input pair, we can select AIN6/AIN7 as the analog inputs for the Mux and then measure the voltage on those pins using the internal voltage reference.

    Regards,

  • 0 in reply to Joachim Wuerker
    TI__Expert 6400 points

    Hi Joachim-san,

    Thank you for your suggestion.

    I have confirmed you're correct.
    Actually, your proposal is effective, but another solution without less S/W change from ADS114S08(reference detection) would be more appreciated.

    Best regards,
    Iwata Etsuji

  • 0 in reply to Iwata Etsuji
    TI__Mastermind 23975 points

    Hi Iwata-san,

    I think any solution to this will require a little S/W change compared to the ADS114S08. I am not sure how else to do it.
    If the reference voltage is close to 0V then the conversion results can be very random. It will most likely be either +FS or -FS depending on the offset of the ADC.

    Regards,