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ISO7730: ISO773x creepage

Hayashi
Expert 1840 points
Part Number: ISO7730

Hi team.

My customer wants to use this Isolator.
they wants to need more creepage is over 9mm in 450Vrms.
However it clear the voltage of 450Vrms, but the creepage is short of 9mm in recommend layout.

Would you tell me the advice if you have good way?
I checked the "Digital Isolator Design Guide", is it only the way it is listed here?

Best regards
Hayashi

  • 0
    TI__Intellectual 2900 points
    Hi Hayashi,

    The maximum creepage achievable for a device will be limited by the package size of the device.
    Our family of ISO78xx devices are available in 2 packages with different creepage/clearance
    (DW > 8mm and DWW > 14.5mm). Please refer to section 6.6 in datasheet "Insulation Characteristics" for additional details.
    www.ti.com/.../iso7830.pdf

    If creepage of >9mm is required, I recommend the ISO7830DWW device

    Regards,
    Anand Reghunathan
  • 0 in reply to Anand Reghunathan
    Expert 1840 points
    Hi Anand,

    Thank you for your advise.
    But my customer wants to keep to use DW PKG, because if it is more big PKG it will become expensive.
    If my customer wants to select the DW because it cannot keep space, what do you have good way?
    ex. the making Notch under the PKG(make creepage)
    Please let me know if there are products that can be recommended at the same level price.

    Best regards.
    Hayashi
  • 0 in reply to Hayashi
    TI__Intellectual 2900 points

    Hi Hayashi,

    I understand customer's concern. Let me try to explain using a diagram.

    Creepage distance between side one and side two of the isolator can be through 2 paths as shown in figure.
    1) Surface of IC -> Packaging Material (creepage >8mm fixed for specific package size)
    2) Surface of board -> PCB Material (can be increased to >9mm with notch/cut on the board)

    The electrical breakdown of different materials can be defined using a parameter called Comparative Tracking Index (CTI).
    The packaging material used for our digital isolator belongs to the highest CTI Material Group (CTI-1).
    Usually, PCB materials belong to CTI-2 category which is lower strength than the CTI-1 material group. Presence of dirt particles on the board can further degrade this rating. 

    A creepage distance through the CTI-1 material is much stronger than the same creepage distance through CTI-2 material. Hence a cut on the board as shown in the figure below will increase the creepage distance through the PCB material and help with the rating of the end system if the PCB material had been the weakest path (which is usually the case).

    Please note that the creepage distance still remains the same 8mm, but it is now through the packaging material which is much stronger in surface electrical breakdown than the PCB material. This should still help in strengthening the effective electrical breakdown voltage.

    Could you please check and let me know if customer requires >9mm creepage along the board or whether he requires the creepage distance through the package of the device?

    Regards,
    Anand Reghunathan