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ISO7760: how to protect output from 4kV surge testing

Chenghu Wang
Prodigy 40 points
Part Number: ISO7760
Other Parts Discussed in Thread: TVS0500, ISO1212, ISO1211

Hello,

I'm using ISO7760 on an interface card. It is powered by 5V and Its outputs are routed to line connector directly. The line interface is subjected to EN61000-4-5 4kV surge testing (with 42 Ohm series resistor).

The signal level is 5V CMOS, so I have to use a TVS with 5V withstand voltage to bypass the surge energy. But the absolutely max. voltage rating of the device is only Vcc+0.5V=5.5V. That means the TVS clamp during breakdown can NOT exceed 5.5V. It's impossible to find such a surge protection, even TIs own TVS0500 can't meet this requirement.

Please advice how to pass the testing without adding too many extra parts/cost.

Thanks.

  • 0
    TI__Expert 6955 points

    Chenghu,

    Our digital isolators aren't generally meant for applications that require such high IEC 61000-4-5 surge requirements.

    We have the ISO1212 or the ISO1211 digital input receiver devices that are meant for applications needing surge protection but 4kV is still very high. The ISO121x family can be powered from the field inputs and output an isolated digital signal.

    Respectfully,

    Lucas

  • 0 in reply to Lucas Schulte9
    Prodigy 40 points

    Hello Lucas,

    The signal under surge protection is an output to the field with 5V logic. ISO12xx won't work.

    -Chenghu

  • 0 in reply to Chenghu Wang
    TI__Expert 6955 points

    Chenghu,

    Unfortunately it does not seem we have solution for 4kV IEC 61000-4-5 protection for 5V inputs at this time without a significant amount of external components. 

    Respectfully,

    Lucas

  • 0 in reply to Chenghu Wang
    TI__Guru 55585 points

    Hi Chenghu,

    Could you please confirm if the surge testing that you are referring to is applied on OUT pins of ISO7760 with respect to its local ground GND2? Or is it with respect to GND1?

    If it is GND2, any reason why you want to test such high surge transient on a CMOS digital output pin? Could you please share more details about your application so that we can if this issue can be addressed differently?

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 40 points

    This is the diagram. To answer your question, it's on GND2.

    The signal will be part of a long cable which is required to undergo Surge by the regulation.

    ISO7760 surge protection.pdf

  • 0 in reply to Chenghu Wang
    TI__Expert 6955 points

    Chenghu,

    Thank you for answering Koteshwar's question about the grounds. Unfortunately we do not have a solution that has 4kV surge protection for a 5V isolator device with CMOS inputs. 

    Respectfully,

    Lucas