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ADS131A04: SIL-Capable by increasing fault detection

JDJ
Expert 4506 points
Part Number: ADS131A04
Other Parts Discussed in Thread: TPS3850

We have a voltage reference REF3425IDBVR connected to REFEXT input in ADC ADS131A04IPBS and are trying to make this configuration SIL-capable by increasing fault detection. If the voltage reference fails in runtime, e.g. changes value from 2.5V to 2.4V, the readings form ADC will be incorrect although from MCU perspective it will be correct reading.

  1. Is there any possibility that the ADC can verify if the voltage reference is within some tolerance, e.g ±1%?
  2. Are you aware of any smart solution I could use in such situation?

Thanks!

  • +1
    TI__Mastermind 23315 points

    Hi JDJ,

    the ADS131A04 itself does unfortunately not have any means to monitor the external VREF voltage.

    I could think of the following options to detect an external VREF voltage out-of-range condition.

    • If you can spare one ADC channel or can place a Mux in front of one channel you could feed the external VREF into that input and then measure the external VREF voltage with ADS131A04 using the internal VREF.
    • Measure the input signal twice, once with the internal VREF selected and once with the external VREF selected and compare the results.
      If at some point the two results don't have the same ratio anymore, one of the VREFs has a fault.
    • Use an ADC inside the MCU to measure the external VREF voltage.

    Regards,
    Joachim Wuerker

  • 0 in reply to Joachim Wuerker
    TI__Expert 4506 points

    It’s isolated design with no spare ADC channels and no spare time for switching over to internal reference. We are considering a window comparator e.g. TPS3850 when no other possibility.

    Please let me know if you have any additional feedback. 

    Thanks!

  • 0 in reply to JDJ
    TI__Mastermind 23315 points

    Hi JDJ,

    I am afraid I don't have any better ideas right now with all those restrictions given.

    Regards,
    Joachim Wuerker