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ISO7721: how to determine the isolation rating in a isolated power converter

Howard Zou
Genius 12365 points
Part Number: ISO7721

Hi,

my customer is designing an LLC resonant power converter. There are two MCUs in the system, one in the transformer's primary side, and the other one is in the secondary side. How do I know if the isolation rating of the digital isolator between the two MCUs is enough, since I don't know the gap of common mode voltage between primary side and secondary side.

  • 0
    TI__Intellectual 2325 points

    Hi Howard,

    Thanks for using the ISO E2E forum!

    The short answer to your question is : the rating is determined based on the transformer specs, which in turn, depend on its design and physical construction (windings, core etc.) from the  transformer vendor.  

    In the situation you described, the ISO7721 provides galvanic isolation for the data/signal path and the transformer provides galvanic isolation for the power path. You can check the transformer datasheet specs to get more information about this. If you wish, you can email me  the schematics/block diagram if any to my email and we can then check and confirm that for you to be 100% sure.

    ===========================

    Alternative options to consider:

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    #1 Products like ISOW78XX provide data isolation *and* integrated isolated power supply in one package. So it's easy to get isolation ratings and certification, all in one simple solution.

    #2: You can use ISO77XX (for data) in conjunction with SN6505 (transformer driver) and an external transformer (for power).

    I hope this is helpful.

    Thanks,

    Abhi