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ISO1211: ISO

Rajat Jain
Prodigy 65 points
Part Number: ISO1211

Hi. We are making a digital input board using ISO1211 IC of TI. We work on high tension lines and 132Kva transformers. Our clients are Indian railways and electric distribution company. We face high transient voltage and surge. I am attaching a design which we have made using ISO1211. Kindly request your inputs on the circuit that we have designed and whether this would protect our board from transient voltage and over current surge. 

. Printing Print Schematic.pdf

  • 0
    TI__Intellectual 1960 points

    Hi Rajat:

    Thanks for posting your question on E2E!

    Functionally, I don't have any concerns with your circuit. However, high voltage transient and the surge is something you'll have to evaluate in your system. Some generic comments are below.

    • I was not able to find the exact datasheet of these input series resistors. Please make sure that the power rating of these resistors are adequate for your application. Alternatively, you may find a suitable Transient Blocking Unit (TBU) for your application.

    • Please make sure that the 1 W rating for RTHR is adequate.
    • SMCJ60CA clamping voltage could be as high as ~100V. Please make sure that the majority of the transient/surge current is dissipated in the SMCJ TVS diode than in the Zener diode. Please select a TVS diode that has a clamping voltage lower than the Zener diode working voltage. However, the voltage seen at the ISO1211 input should be less than 60 V to maintain the device absolute maximum voltage rating.

    Regards,

    Dushmantha

  • 0 in reply to Dushmantha Rajapaksha
    Prodigy 65 points

    Thank you Dushmantha for promt response. Do you suggest we remove the TVS diode and use TBU instead to protect our circuit? 

  • 0 in reply to Rajat Jain
    Prodigy 65 points

    Our solution is to sense  AC/DC input voltage (upto 300V). Could you suggest what can we change to ensure we protect against high transient and protect ISO1211 and other circuitry?

  • +1 in reply to Rajat Jain
    TI__Intellectual 1960 points

    Hi Rajat:

    Thanks for providing the additional information!

    For 300V AC/DC input voltage, you may find this tech note useful. As you can see from the Figure 3 of the tech note, you may be able to use lower voltage full-bridge rectifier diodes by moving RTHR in front of the diodes.

    For transient/surge protection, TBU-CA0065-200-WH is an example for a TBU that may work. You'll need both TBU and TVS diodes for the protection scheme to work. Also, you may reach out to the TBU manufacturer for other recommendations.

    For the TVS diode, please pick the lowest working voltage diode that doesn't interfere with your normal operation. SMCxx(C)A family is good.

    Regards,

    Dushmantha

  • 0 in reply to Dushmantha Rajapaksha
    TI__Intellectual 1960 points

    Hi Rajat:

    I'm hoping that I was able to answer all your questions. Please feel free to reply to this thread or click on "Ask a related question" button on top if you have further questions.

    Regards,

    Dushmantha