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ISO7741: Isolation Design with ISO(W)774x/GDT clearance

Jim Hsiao
Prodigy 10 points
Part Number: ISO7741
Other Parts Discussed in Thread: ISO7740, ISOW7741

Tool/software:

Now I used ISOW7741 & ISO7740 for isolated RS232 design.

According to the "IEC60601-1-2 Compliant Digital Isolation Design with 16-kV Contact Discharge ESD Protection".

The recommended GDT is the 2093-250-SM. However, the moat can only be 2.5mm.

But The DW-16 SOIC package with 8-mm clearance is capable of supporting an ESD.As far as I know, at least 4mm of clearance is required.

Should I use this GDT or would you recommend another part or a DIP type instead?

  • 0
    TI__Expert 7495 points

    HI Jim,

    Thank You for reaching out. Encouraging to see the App Note coming to use in your design.

    Please find my inputs below:

    Jim Hsiao said:
    But The DW-16 SOIC package with 8-mm clearance is capable of supporting an ESD.As far as I know, at least 4mm of clearance is required.

    Clearance really depends on the ESD Level Protection that you're targeting. If the the target is 15kV and above then >12mm Clearance is required without any GDT across isolation

    If your requirement is 16kV, you can go ahead with with recommended GDT in the Appnote, 2093-250-SM. 

    Regards
    Varun
  • 0
    Prodigy 10 points

    Hi Varun,

    Thank you for your response. Please allow me to clarify my question.
    This case is applied in medical instruments, and IEC 60601-1 mentions that Hi-Pot 1.5kV electrical isolation must be met.
    As far as I know, under these conditions—Pollution Degree 2, FR4 material, and a working voltage of 1.5kV—the clearance distance should be at least 4mm.

    As I mentioned earlier, the clearance distance of the 2093-250-SM is only 2.5mm.
    Using this GDT will not maintain the required 4mm clearance.
    Should I continue using this GDT and maintain the 2.5mm clearance, or do you have any other suggestions?

    Regards

    Jim

  • 0 in reply to Jim Hsiao
    TI__Expert 7495 points

    Hi Jim,

    Thanks for the details.

    I'm not fully aware of the 4mm clearance requirement as per IEC 60601-1 standard and how does it really affect the Isolation performance. 

    If the 4mm clearance is a must then a higher clearance GDT might be unavoidable but I don't have a part number to suggest right now for this as we have tested only for 2093-250-SM with 2.5mm of clearance

    Regards
    Varun