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ISOW7841: EMI Immunity and shielding

Rene Bakker
Intellectual 500 points
Part Number: ISOW7841
Other Parts Discussed in Thread: ISO7741

Hello,

The SLLA368C application note is very useful for the EMI emission related issues. The ISOW7841 datasheet also states "The ISOW784x family of devices provides high electromagnetic immunity and low emissions while isolating CMOS or LVCMOS digital I/Os.". So what is known about this high electromagnetic immunity? for example related to EN 61000-4-3?

Our application needs 4kV isolation and to be immune to 20V/m (up to 1GHz), 10V/m (up to 2GHz), 5V/m (up to 2.7GHz) and 3V/m (up to 6GHz). What can we expect of the susceptibility of the ISOW7841 to these EM-field strengths? Can the ISOW7841 withstand these immunity tests or should we take some kind of extra precaution.

Preferably we like to use the ISOW7841 in an unshielded plastic enclosure, since using metal EMI shields usually makes a 4kV isolation much more difficult. Or can the ISOW7841 only withstand these EM-fields using extra shielding. If so, what advice can you give on how to implement such an EMI shield, like for example to which GND side should it be connected, etc.

Kind regards,

René

  • 0
    TI__Guru 55885 points

    Hi Rene,

    Welcome to TI E2E forum and thank you for showing interest in ISOW7841 and also for going through the application note SLLA368C.

    Since ISOW7841 (digital isolator with integrated power) is a more sophisticated device than other digital isolators (like ISO77xx), the EMI performance of ISOW7841 may not match that of ISO77xx but is expected to be superior to other equivalent devices in the industry.

    With respect to Radiated Immunity (RI) performance, we currently don't have an elaborate testing conducted on ISOW7841. Our limited test data indicates that ISOW7841 supports 10V/m upto 1GHz on a medium size evaluation board. We do not have test data for frequencies >1GHz. To be able to support 20V/m, you may require additional shielding.
    If RI is a hard requirement and you do not like to use any EMI shields then I recommend to use ISO7741 along with external SN6505 based power supply. This should support 20V/m.

    Since ISOW7841 switches at very high switching frequency (~60MHz), based on your radiated emissions (RE) requirement you may have to optimize your PCB to meet your RE requirements. Please do refer to the below E2E post for some details on optimizing your PCB to support good RE results. Let me know if you have any questions, thank you.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Intellectual 500 points

    Hello Koteshwar,

    Thank you for your reply and suggestions. Especially the radiated emissions common-mode chokes update.

    Regarding the radiated immunity, can you provide these limited radiated immunity test data for the ISOW7841? So including e.g. the used test board.

    Do you also have an application note, test report, white paper, or something else, which addresses the ISO7741 in relation to the 20V/m radiated immunity tests? And does this include the SN6505?

    Kind regards,

    René

  • 0 in reply to Rene Bakker
    TI__Guru 55885 points

    Hi Rene,

    Sure, I can help you share more information related to the RI testing. Can I reach out to you on your email that you have used to create your E2E account? Thanks.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Intellectual 500 points

    Hello Koteshwar,

    Thank you. Yes you can use that e-mail address.

    Kind regards,

    René