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Original question:

ISOW7841EVM: ISOW7841EVM

ISOW7844: EMC questions

Lei Lu
Prodigy 10 points
Part Number: ISOW7844
Other Parts Discussed in Thread: ISOW7744, ISOW7743

Hi,

We were initially using the competitor of ISOW7844 on one of new project in developing and saw similar Emission spikes as in the figure.3 of SLLA368C. So we are considering to change to ISOW7844 and have this questions:

Per SLLA368C, use 3.3V input supply if possible. Currently our design is 5V in / 5V out. If it is changed to 3.3V in / 5V out, would it be better for EMC? Or it would only be improved with 3.3V in / 3.3V out?

SLLA368C suggests to use interlayer stitching capacitance, but we will have trouble to use this strategy but still meet separation distance requirement for medical device requirement (IEC 60601-1), but we can apply stitching vias along the board edges. But I don't see much explanation in SLLA368C regarding this mitigation method, but just a note in Figure 6. Please let me know that also helps.

Thanks,

  • 0
    TI__Guru 53945 points

    Hi Lei,

    Welcome to TI E2E forum!

    Thanks for reaching out and for sharing details related to your questions.

    Lei Lu said:
    If it is changed to 3.3V in / 5V out, would it be better for EMC? Or it would only be improved with 3.3V in / 3.3V out?

    3.3V to 3.3V will yield the best radiated emissions results while 3.3V to 5V will mostly be similar to 5V to 5V. Hence, our recommendation is still to use 3.3V to 3.3V if this is an option in your application.

    The radiated emissions improvement with stitching vias is really small and hence not much importance given to that approach.

    ISOW78xx is our first-generation ISOW device family while now we have the second-generation family ISOW77xx. The ISOW77xx offers significantly better performance over ISOW78xx especially on the radiated emissions. Even though ISOW78xx and ISOW77xx are not pin-compatible, we recommend customer to consider ISOW77xx in place ISOW78xx achieve good emissions results. ISOW77xx can meet the emissions requirements by most applications by just using ferrite beads and no stitching cap would be need.

    https://www.ti.com/product/ISOW7741

    Please see below E2E for more details on comparison between ISOW77xx and ISOW78xx, thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 10 points

    Hi Koteshwar,

    Thanks for the comments. 

    I do need at least 3 channels of inputs, so either ISOW7743 or ISOW7744 could be used. But both of them are in preview status. Will TI provide samples for testing at this point? If so, could you or local FAE please contact me in email to discuss the detail delivery time? 

    Thanks,

  • 0 in reply to Lei Lu
    TI__Guru 53945 points

    Hi Lei,

    Thanks for your inputs.

    Yes, even during PREVIEW status the samples of devices can be requested or ordered. Please place your request from the ordering section of ISOW7744 product page. I am also copying a direct link below for your quick reference. Let me know if there are any further questions, thanks.

    https://www.ti.com/product/ISOW7744#order-quality


    Regards,
    Koteshwar Rao