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UCC21540: isolation damaged in case of faulty overheating?

Genius 12445 points
Part Number: UCC21540

Hello Team,

will the isolation barrier stay functional in case of thermal overheating? 

This is required by DIN EN 61800-5-2 (table D.13 – opto-coupler) and as well in EN ISO 13849-2:2003 (table D.20 - opto-coupler). Basically it says that a failure of the isolation barrier cannot cause an overheating.

And may I ask you to explain below data sheet specification, Chapter 7.8, page 8, please?

Does that mean the external primary side power supply has to power limited to get VDE approval? According to fig. 7.3 that would be about 700mW at 100°C?

Thanks and Best Regards,


  • Hello Hans,

    Thank you for reaching out on E2E. 

    With regards to your first question, UCC21540 is not covered by the standards you mention, as it is not optically isolated. This part is certified to the DIN V VDE V 0884-11:20177-01 standard for capacitive isolation. You can find more information on our isolation technology here:

    That said, datasheet section 7.8 specifies that the isolation barrier is guaranteed up to 150C.

    For your second question, these specifications are to protect the isolation barrier in case of a failure. If the current and power are not limited a failure in the input or output circuitry could cause excessive overheating leading to further damage. You are correct, at 100C the power should be limited to 700mW. This article goes into more detail on the meaning and purpose of these ratings:

    Please let me know if this answers your question by clicking the green button, or let me know how I can continue to help.