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ISOW7840: Inquiry of PCB layout

MESH
Intellectual 830 points
Part Number: ISOW7840
Other Parts Discussed in Thread: ISO7841, ISO7741

Hello,

I am considering PCB layout that is used ISOW7840 and ISO7841.

I confirmed figure 21 of ISO7841 datasheet. (Cross section of PCB layout)

The datasheet recommends "keep free bottom area of ISO7841".

I am considering to mount ISOW7840 and ISO7841 or ISOW7840 same position of top layer and bottom layer on this PCB to reduce board size. (Overlap position)

The thickness of PCB is 1.6mm and another signal pattern does not place bottom of ISOW7840 and ISO7841.

I want to know if ISOW7840 and ISO7841 are at risk of interfering with each other and causing malfunctions.

Regards,

MESH

  • +1
    TI__Mastermind 49445 points

    Hi MESH,

    Thanks for reaching out.

    MESH said:
    The datasheet recommends "keep free bottom area of ISO7841".

    That's right, the PCB underneath device need to be kept free from any traces or vias to achieve full device isolation specifications. This is not specific to ISO7841 but this is a requirement for any isolator to meet the required creepage/clearance. If the isolation or creepage/clearance requirements are lower, then the spacing can be reduced. This completely depends on the application isolation requirements and doesn't depend on ISO7841 or ISOW7840.

    MESH said:
    I am considering to mount ISOW7840 and ISO7841 or ISOW7840 same position of top layer and bottom layer on this PCB to reduce board size. (Overlap position)

    Overlapping devices on the top and bottom is not an issue and it doesn't necessarily require routing underneath device, hence it doesn't cause any compromise in meeting isolation requirements.

    MESH said:
    I want to know if ISOW7840 and ISO7841 are at risk of interfering with each other and causing malfunctions.

    There is absolutely no risk in using ISOW7840 and ISO7841 in top and bottom, the device is going to work normal. Even if there are PCB traces or vias underneath device, it still doesn't interfere with device operation and both devices will operate normal without any issues. The traces or vias only affect overall system creepage/clearance distances which may or may not be important for an application.

    I hope this answers your questions, thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Intellectual 830 points

    Hi Koteshwar,

    Thank you for your reply.

    Your reply is very helpful for me.

    Regards,

    MESH

  • 0 in reply to Koteshwar Rao
    Intellectual 830 points

    Hi Koteshwar,

    After that I checked the market stock quantity of ISO7841.

    Unfortunately, the market inventory quantity was less than the required quantity.

    I am considering ISO7741 as a replacement part.

    I'm guessing that what I asked the other day also applies to ISO7741.

    Let me confirm your opinion just in case.

    Regards,

    MESH

  • +1 in reply to MESH
    TI__Mastermind 49445 points

    Hi MESH,

    Yes, that is correct. Everything I have mentioned about in my first response regarding ISO7841 also applies to ISO7741. In fact, these are applicable to most digital isolators as the main function of all these devices is isolation. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Intellectual 830 points

    Hi Koteshwar,

    Thank you for your reply.

    I will use ISO7741 as a replacement parts.

    Regards,

    MESH