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ISO7761: Creepage/clearance for 1.000VDC measurement device

user5877758
Prodigy 30 points
Part Number: ISO7761
Other Parts Discussed in Thread: UCC12050, ISO7820, ISO7810, ISO7840, ISO7841, ISO7842, ISO7821, ISO7741, SN6505B, SN6505A

Hi support team,

I am using the ISO7761 DW-16 together with the UCC12050 to isolate my voltage measurement circuit from my µC-mainboard. The voltage measurement range is to be 1.000VDC. Now I went to a accredited test lab to verify the safety of my system based on EN61010-1. They came back to me saying that a minimum creepage of 10mm and a minimum clearance of 10.5mm according to EN61010-1 is required. The reason is that reinforced isolation is needed and that means the requirements for creepage/clearance need to be doubled.

Now the problem is that both ISO7761 and UCC12050 provide only roughly 8mm creepage/clearance.

What can I do to satisfy this requirement?

Thanks,

Martin

  • 0
    TI__Guru 53715 points

    HI Martin,

    Welcome to TI E2E forum!

    I took a quick look at Table 7 in IEC 61010-1 and I do see that creepage required for 1000Vrms working is 5mm for basic isolation and is twice (10mm) of that for reinforced isolation. While clearance requirement from Table 6 only requires 2.52mm for 1000Vrms working voltage for basic isolation and is twice (5.04mm) of that for reinforced isolation.

    To meet 10mm creepage requirement, you could use the DWW-16 package that is available with ISO78xx family and with ISO7741 device. Unfortunately, we do not have 6-channel version in DWW package but we do have 4-, 2- and 1-channel versions of ISO78xx in DWW-16 package, i.e., ISO7840, ISO7841 and ISO7842, ISO7820, ISO7821 and ISO7810.

    For power supply, you could use SN6505A / SN6505B based external transformer solution where you could choose transformers with required creepage and clearance requirements. The below list of transformers from Wurth support 11mm creepage / clearance and work with SN6505A. Please see below snapshot from datasheet for more details.

    I believe you now have suitable options to choose from. Let me know if you have any questions, thanks.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 30 points

    Hello Koteshwar,

    thank you for your quick response.

    Let me double-check with the guys from the lab. If you're right (which is what I assume) we would only need to increase the creepage. That could be done by carving/cutting the PCB.

    Thanks a lot!

    Martin

  • 0 in reply to user5877758
    TI__Guru 53715 points

    Hi Martin,

    Yes, by carving / cutting grooves on PCB you can increase the creepage of PCB but the overall creepage will still be limited by the device which is 8mm.

    Cutting grooves on PCB is a common practice because material group of PCB  is usually like "MG IIIa / IIIb" and hence, the grooves help achieve higher creepage for PCB. While device with material group "MG I" need not have very high creepage and can still meet most requirements as is. Device and PCB with different creepage values can still be used to meet overall isolation independently.

    In your case, it seems like 8mm creepage of "MG I" device itself is not sufficient and hence, this needs to be increased to >10mm by choosing a larger package to meet EN 61010-1 requirement. DWW-16 package should help meet these requirements.

    Based on the material group of your PCB, you might still need the grooves to achieve >>10mm creepage if the PCB is not built with "MG I" material. Thanks.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 30 points

    Hi Koteshwar,

    I understand! So carving is not an option.

    Can I use a coating for ISO7761 and UCC12050 so I will move it to Pollution Degree 1 which would decrease the required creepage distance significantly.

    Thanks,

    Martin

  • 0 in reply to user5877758
    TI__Guru 53715 points

    Hi Martin,

    Carving grooves might still be needed to make the PCB meet your application creepage requirements but this alone might not be sufficient to make your solution meet overall creepage requirements.

    Yes, coating both ISO7761 and UCC12050 is definitely an option and should enable you meet your decreased creepage requirements. If this is an option then I would recommend to go with this. Thanks.

    Regards,
    Koteshwar Rao