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Read analog voltage isolated

Other Parts Discussed in Thread: ISO1211, ADS7142, AMC1311

Hi,

I have to read with galvanic isolation a supply voltage that can reach 60V. The voltage read must be sent to a uC (the uC is already galvanically isolated from the supply voltage).
i am availabel to both analog and a digital approach with the reading of a voltage threshold with relative digital signal for the uC.

Which solution do you recommend me? Should you direct me to the ADC forum?

BR,

Antonio

  • Hi Antonio,

    Did you mean to say that you only need to find out if the power supply voltage is above or below a particular voltage, like for the Binary Input Module? If yes then, using ISO1211 might be a good single-chip solution.

    If you needed to read the absolute voltage of 60V inputs signal then you would have to follow the traditional analog or digital isolation approach. I believe the input voltage needs to be brought down before it is connected to the isolator.
    Customer would have to make the choice on which option suits him the best. Digital isolation gives him with many options of ADCs and isolators to choose from but is going to be a multi-chip solution. While Analog isolation might need just one device assuming the ADC of the MCU is used to convert the isolated analog signal to digital. The Analog solution may not give you as many options as the digital solution.

    I will notify the precision ADC team first to check if Analog solution is sufficient to meet customer requirement. Thanks.

    Regards,
    Koteshwar Rao

  • Thanks Koti.

    Agreed if a binary output is the requirement, then the ISO1211 is the best fit.  If you need more resolution we can scale the voltage down using a resistor divider and then pass it over an isolation barrier with the AMC1311 to be acquired by an MCU ADC, or general purpose ADC such as the ADS7142.

  • Hi All,

    ISO1211 looks like a good component but I don't know if it is precise enough because customer has to detect thresholds (for example from 25V or 55V) with good precision (certainly below the volt) and little variable depending on the temperature.

    Kindly waiting for your feedback.

    BR,

    Antonio

  • Hi Antonio,

    I am not sure about customer precision requirements but since the ISO1211 is targeted to be used with digital field inputs, it has Schmitt trigger inputs with VIH and VIL thresholds and these thresholds will have some variation. Please see below the VIH and VIL specifications from ISO1211 datasheet electrical specifications table for given RTHR resistors and let me know if this is acceptable to customer.

    To support higher input voltages, RTHR can be further increased and you can use the calculator provided on ISO1211 product folder to estimate RTHR values. I am copying below the link to ISO1211 calculator.

    If these input thresholds variations are not acceptable to customer then they might have to go with the traditional approach of using ADC & digital isolator or by using an isolator that can accept analog voltage (like AMC1311). Let us know which one works best for customer, thanks.

    Regards,
    Koteshwar Rao