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Original question:

ISOW7742: Can ISOW7742 support VDD=3.3V, VISOOUT=5.0V configuration?

ISOW7742: protection for 4kV?

Stefan Lintner
Expert 4955 points
Part Number: ISOW7742

Hi team,

customer is using ISOW7742 in a design to give 2MOPP protection for max mains voltage. So creepage and clearance should be 8 mm. 

there are very few discharge tubes that fit the requirements, that is, it spark over at a voltage above 4000 V, and fit the creepage and clearance distance. How would you protect the isolator against ESD charges in this case? I am wondering if you have seen solutions for this?

BR,
Stefan

  • +1
    TI__Guru 55575 points

    Hi Stefan,

    Thank you for reaching out.

    Assuming 4000V that you are referring to is isolation voltage test that lasts for a few seconds, I confirm that ISOW7742 supports upto 5kVrms and this is specified in Insulation Characteristics table of ISOW7742 datasheet as Withstand Isolation Voltage (VISO).

    Since the device supports 8mm creepage and clearance, we don't see any arc over or sparking happen during the test. Each unit is production tested for VISO, hence, this shouldn't be an issue.

    Stefan Lintner said:
    How would you protect the isolator against ESD charges in this case?

    Let me know if there is any specific ESD level that customer is trying to meet. ISOW7742 supports 8kV ESD contact discharge which I expect to be sufficient for your customer.

    Let me know if you have any other questions, thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    TI__Expert 4955 points

    Hi Koteshwar,

    customer is concerned that side B can become ‘charged up’ by an ESD pulse with respect to side A. As the medical standard gives up to 15 kV ESD pulses, I think that side B can differ up to 15 kV with respect to side A. And this is higher than the isolation strength of the part.

    They are referring to this app note: 

    IEC60601-1-2 Compliant Dig. Iso Design W/ 16-kV Contact Discharge ESD Protection

    BR,
    Stefan

  • 0 in reply to Stefan Lintner
    TI__Guru 55575 points

    Hi Stefan,

    Thank you for sharing more details related to ESD requirement.

    As described in the app note that you attached, 15kV ESD requires a clearance of >10mm. Since the DW package of ISOW7742 has a clearance of 8mm, it cannot support 15kV ESD. Since the clearance requirement is not met, the air across the barrier is going to break first cause electrical sparks.

    To avoid such electrical sparks, please request customer to follow the suggestions provided in the app note that you included in your post. Let me know if you have any further questions, thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    TI__Expert 4955 points

    Hi Koteshwar,

    which brings me to my original questions: Which GDT would you recommend which spark over at a voltage above 4000 V?

    BR,
    Stefan

  • +1 in reply to Stefan Lintner
    TI__Guru 55575 points

    Hi Stefan,

    As suggested in the App Note that you referred, we recommend to use GDT 2093-250-SM from Bourns. I am copying below a snippet from the App Note related to the part number of GDT. Thanks.


    Regards,
    Koteshwar Rao