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ISOW7841: can't pass EMI test

Part Number: ISOW7841

We use ISOW7841 in the BMS product,used for isolate ADC's SPI interface.

We test EMI,and find at 400M frequency,it is 50~60dbuV/m, can't pass CLSS 4.

when we take off  ISOW7841,EMI CAN pass.

Pls give us design suggest,thanks!

  • Hi,

    We've had some issues with ISOW7841 with EMI, though in a lower frequency range.
    You should start by reading Application Note SLLA368A, if you haven't already. There is good information there.
    We made some improvements using the techniques shown but still can't get emissions as low as we want.

    Alex.
  • In reply to Alex Ballantyne:

    Hi Alex,
    Thank you for pointing to the application note SLLA368A, this sure is the right place to start from.

    Hi User5195153,

    Even though ISOW7841 is the source of radiations, the overall EMI performance on an end product depends a lot the PCB size and the cables connected to the PCB. Larger PCB size and cables connected the emissions from ISOW7841 much higher than what it would have been without them. Hence to bring down emissions, like Alex mentioned in his earlier post we recommend you to go through the application note SLLA368A. I have shared a link to the same below.

    www.ti.com/lit/an/slla368a/slla368a.pdf

    Since your application is automotive where the emissions standard CISPR 25 is much more stringent than the industrial emissions standard, the most important thing to do to achieve reduction in emissions is to implement a stitching capacitor using PCB layer as described in SLLA368A. The capacitance of the capacitor needs to be at least 30pF and for it to be more effective anything >50pF is recommended.

    Once you use the stitching cap, you should see a significant improvement in over emissions performance.
    Let me know if you have any other questions, thank you.


    Regards,
    Koteshwar Rao
  • In reply to Koteshwar Rao:

    Thanks Alex and Rao!!

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