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Original question:

ISO7720: D package reinforced isolation

ISO7741E-Q1: reinforced insulation

Bernhard Baier
Prodigy 30 points
Part Number: ISO7741E-Q1
Other Parts Discussed in Thread: ISO7741, , ISO7741-Q1, ISO7841

Dear experts,

the ISO7741 is rated for reinforced insulation for a maximum of 800V. The internal device parameters would allow a maximum working voltage of 2121V DC which should be sufficient to achieve a reinforced rating of 1000V DC. So I guess the reason for the reduced reinforced rating is the insufficient creepage over the body of the IC. Is there a variant capable of a reinforced insulation of up to 1000V dc?

Alternatively are there other digital insulators suited for this use case (I couldn't find any when searching especially for reinforced insulators)?

The only way to get a reinforced insulation of 1000V DC with the ISO7741 would be to have a type 2 coating according to IEC 60664-3. Is that correct?


Yours sincerely

Bernhard Baier

  • 0
    TI__Mastermind 49415 points

    Hi Bernhard,

    Thanks for reaching out and for showing interest in ISO7741E-Q1.

    Please note that the criteria for qualifying an isolator for a given voltage of reinforced isolation varies by the certification agency, hence, it is important to know which standard does your end equipment need to be certified for.

    The criterion for VDE 0884-11 to qualify an isolator to be supporting reinforced isolation is minimum surge capability of 10kV (tested as per IEC 62368-1). ISO7741 meets 12.8kV of surge (with VIOSM being 8kV with 60% margin considered) and also supports maximum repetitive peak isolation voltage (VIORM) of 2121Vpk or in other words, maximum working isolation voltage (VIOWM) of 1500Vrms. These are reinforced isolation ratings as per VDE.

    ISO7741E-Q1 is a special part that supports AEC-Q100 Grade 0 temperature range of -40C to 150C ambient. ISO7741-Q1 with a AEC-Q100 Grade 1 device with temperature range of -40C to 125C while ISO7741 is an industrial grade device.
    If you are looking for a higher creepage device then we have ISO7841 available with DWW package that supports 14.5mm of creepage.

    Let me know which one of the above meets your requirement and do let us know what certifications are needed as per your end equipment requirement, thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    TI__Mastermind 49415 points

    Hi Bernhard,

    Could you please help us with the information requested in my previous response? If my previous response already addresses your question, please let me know so that I can go ahead and close this thread. Thanks.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 20 points

    Hi,

    thank you for your response. I am Bernhard's colleague and working with him at this project. Bernhard is currently on vacation.

    Within our battery management application, we only have to meet the insulation requirements of the IEC 60664-1. Therefore, our requirement is reinforced insulation for 1000Vdc and pollution degree 2, which demands a 10mm external creepage distance. Since we need a device with FIT rates, the ISO7741 is the preferred component with its DW package. To implement the ISO7741, we are considering potting to reduce the pollution degree to 1 in accordance to IEC 60664-3. In consequence, the required creepage distance decreases to 6,4mm, which the DW package provides. In terms of the temperature range, the digital isolator has to operate between -40°C and 85°C.

    Let me know what you think about our considerations.

    Best regards,

    Matthias Schmid

  • 0 in reply to Matthias Schmid
    TI__Mastermind 49415 points

    Hi Matthias,

    Thank you for sharing additional information about your application requirements.

    The approach that you have mentioned to reduce the pollution degree to 1 by potting the device should be fine and should enable you meet your requirement.
    Alternatively, if it is of your interest, you could also consider using ISO7841 in DWW package that offers 14.5mm creepage while all other specifications of ISO7841 will be either similar or better compared to ISO7741. Please do also note that ISO7841 is only available in industrial grade while ISO7741 is available in automotive grade as well.

    Both devices support -55C to 125C operating temperature range and choosing either of the solutions should be fine. Thanks again for reaching out and showing interest in TI digital isolators.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 20 points

    Dear Koteshwar,

     

    Thank you for your feedback!

    From my side, everything is clear now how we can apply the ISO7741. The industrial grade is sufficient, however the ISO7741 provides detailed functional safety information and is admittedly cheaper.

     

    Best regards,

    Matthias Schmid

  • 0 in reply to Koteshwar Rao
    Prodigy 30 points

    Dear Koteshwar,

    is there any approval, that the ISO7741 is only limited to a working voltage of 800V for reinforced insulation per EN60950-1:2006/A2:2013 because of the reduced creepage of >8mm or are there any internal limitations by the DW package? Alternately can it be approved by TI that the ISO7741 can be used for 1000V reinforced insulation with appropriate coating?

    Is there a version of the ISO7841 in DWW package that is capable for beeing used in safety relevant applications (that's the reason why we choose the automotive variant of the ISO7741)? Via the MTBF/FIT estimator we where able to check, that all values are equal to the ISO7741-Q1 but the documentation is not present for the ISO7841.

    Kind regards,
    Bernhard Baier

  • +1 in reply to Bernhard Baier
    TI__Mastermind 49415 points

    Hi Bernhard,

    All the certificates of ISO7741 are listed in their respective page on TI website under the section "Technical Documentation"  under the sub-section "More Literature". Please allow me to check with the TI internal certification expert to see if there is a certificate that explicitly mentions ISO7741 working voltage rating.
    1000V reinforced insulation with appropriate coating approval should come from the respective certification agency, as they will have provide you the final certification for your product. Please reach out to the respective certification and get their approval to use coating to bring down pollution degree.

    I believe you are referring to Functional Safety documentation that is included for ISO7741-Q1 on its product page. Such Functional Safety document is only made available for automotive grade parts and it currently doesn't exist for industrial grade parts. Hence, we do not have such a document for ISO7841.

    Since you are specifically looking for Q1 grade parts that have Functional Safety document available, I would like to ISO7741-Q1 is also available in DWW package (full part number -> ISO7741QDWWRQ1) which supports higher working voltage. The functional safety document will also be applicable to DWW package variant as well. Please let me know if this is something that meets all your requirement?


    Regards,
    Koteshwar Rao

  • +1 in reply to Koteshwar Rao
    TI__Mastermind 49415 points

    Hi Bernhard,

    I reached out to certification expert and here I have information related to the certificates.

    The TUV certificate from ISO7741 product page (link below) under "Technical Documentation" section categorized under "More Literature" has the information that you are looking for.

    ISO7741 Product Page -> Technical Documentation

    The TUV certificate lists 800V reinforced isolation working voltage for ISO7741 in DW package on page 8 and similarly, lists 1450V for DWW package on page 10. These ratings are according to EN/UL/CSA 60950-1 as listed in the header of the column.

    I hope this answers your question, thanks.


    Regards,
    Koteshwar Rao