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iCoupler ADuM524x CTI-value


I use an iCoupler ADuM5242 in a device that is currently under test at UL.

Regarding the safety clearances, the UL inspector does not accept the CTI value of 175V described in the document. He says it was not tested under UL and so, he cannot accept the described value issued by the document.

The application has got on the lower side a circuitry that is connected to SELV. The iso side is connected to 250V at the most.

Is there any argument I can express that the ADuM5242 is suitable nevertheless?

Thanks for your help.

Regards, Andreas

  • Andreas:

    I have asked our expert on isolation and certification about this and here is his response:

    Yes, this part should meet the requirements for single protection.  According to IEC60664-1, the insulation coordination standard, SELV is <60V so we are looking at a total of 310V max for the cross barrier and even under Material Group III that only requires 3.2mm of creepage.  The impulse requirement is 2500V peak for Over Voltage Category II.  These parts are rated for 2500Vrms transient withstand which covers peak voltages of 3500V.  I think these will be adequate.  


    There are newer parts than the ADuM524x, with better efficiency and lower power requirements, I would recommend the ADuM5210 even though the board space is a little larger.

    Regards, Brian

  • Hi Brian,

    thank you for your prompt answer.

    UL requires at this spot reinforced protection and the needed space will be @250V 2.5mm x2=5mm according the regulations 61010.

    Is the CTI ranking not tested by UL?

    Regards, Andreas

  • Andreas:

    I asked again our isolation expert and here is the response:

    For reinforced you will need to determine the material group.  It is Group II based on the enclosed Letter of attestation from CSA and VDE.1325.2701138 Attestation.pdf0576.G770HCD_G720D_G700LY VDE CTI 224198(1).pdf

    By my calculation for material group II, pollution degree II, installation class II, the creepage required is 3.5mm.

    The ADuM524x has 4mm of creepage.

    Regards, Brian

  • Hello Brian,

    I really appreciate your effort to help me. Thank you for sending me the link for the material description.

    How can I prove that the material in the document is used in the ADuM524x chips? There is no reference in the material document or in the data sheet of the chip, as far as I can see. UL did not even accept the description in the data sheet ...

    UL requires reinforced insulation at this point. Regarding table 7 of DIN EN 61010 at 250V the gap has to be 2,5mm for basic insulation and 5,0mm for reinforced insulation for material group II and pollution degree II. Do you have a different standard?

    Regards, Andreas

  • Andreas: For 250Vac under 61010 Table 7 the correct creepage for Pollution degree II material group II is 1.8mm Basic and 3.6mm Reinforced. See attached.

    Regards, Brian

  • Hello Brian,

    you're right because you take material group II as given. UL does not accept group II but III. So, I have to face 5,0mm as reinforced protection. And by this, ADum524x doesn't fit anymore...

    I send the material data sheet to our UL inspector and I will wait what happens.

    In the meantime, I will check your suggestion ADuM 5210 as an alternative.

    Again, thank you for your help.

    Regards, Andreas