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ISO7721: Injection current

Konrad Holzmann
Prodigy 150 points

Part Number: ISO7721

Hello,

we have some trobules with overvoltage situations on pins OUTA and INB. In our case we use a 3.3V protection diode on these pins, but in some situations we have device failures. In this case VCC1 and GND1 get shorted in the ISO7721.

To do some further protection I need to know the maximum allowed current injected on OUTA and INB for e.g. 500ms. 

My idea, current runs into device, through protection diode to VCCI. VCCI gets a shunt referece to limit the voltage to e.g. 4.7V. 

Thanks!

Regards Konrad

  • 0
    TI__Mastermind 21525 points

    Hi Konrad,

    Thanks for reaching out.

    The absolute maximum ratings specify 15mA maximum load can be applied without device damage. Any current that exceeds this can cause damage to the device.

    This is primarily for the output pins. Please allow me to check with my team to confirm your question.

    Regards,
    Aaditya

  • 0 in reply to Aaditya V.
    Prodigy 150 points

    Hello Aaditya,

    I would like to know the allowable current in these diodes:

    Thanks a lot!

    Regards Konrad

  • 0 in reply to Konrad Holzmann
    TI__Mastermind 21525 points

    Hi Konrad,

    Thanks for the clarification on the specific diodes you are referring to.

    The highlighted diode is designed to bypass an ESD pulse when such a pulse happens to appear at the input pin. The ESD voltage rating that the device supports is listed out in datasheet. Since the diode is not designed to be operated with a continuous current, it doesn't have a continuous current rating defined.

    if you would still like to have protection like an external series resistor to limit current into device for accidental fault conditions to higher voltages, then I would recommend to choose the resistor value such that the current through this diode is <1mA to make sure the diode is not stressed out much during such accidentally momentary faults.

    Regards,
    Aaditya

  • +1 in reply to Aaditya V.
    Prodigy 150 points

    Hello Aaditya, thanks a lot. Will try to use a resistor that is large enough. Regards Konrad