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Compliance with IEC 61000-4-6 on digital interfaces

Kaveh Mohammad
Intellectual 585 points

Hi, 

I have ethernet and RS485 interfaces in my design. My design requires compliance with IEC 61000-4-6 at 3Vrms exposure. 

Is there an IC from TI which can act as the interface with my digital circuit and outside to provide such protection? Or any TI app note with advise toward such design compliance would be appreciated, 

Thanks

  • 0
    TI__Guru 52382 points

    Hi Kaveh,

    So none of the RS-485 transceivers that we carry are directly specified to IEC 61000-4-6; its not a standard we test for in-house for RS-485. 

    That being said - we have worked a little bit with applications that are trying to meet these goals - and generally it will line up pretty well with our basic EMC mitigation techniques.

    While this reference design doesn't directly work with 4-6 - a lot of the methods discussed are ones we'd suggest if you are trying to meet this standard.

    Reference Design: https://www.ti.com/lit/ug/tidue61/tidue61.pdf?ts=1706124820438&ref_url=https%253A%252F%252Fwww.google.com%252F

     

    Please note that the IC used in the design above can be replaced with pretty much any  RS-485 device since most of them have identical pinouts and pin-functions and only differ on a few key specs. 

    The one element that is not mentioned in the above reference design is the use of a common mode choke - which is also common (I'd argue more common than filter caps to ground on the differential bus and personally I have seen better results with because there are fewer tradeoffs than there are with filter caps from a technical perspective - the filter caps are shown in the above document).

    That being said what are the requirements of the RS-485 portion of the system - I understand the IEC requirement, but what about the RS-485 bus itself? 

    1. What voltage supplies do you have available (3V to 5.5V)

    2. What speed is required (up to 50Mbps)

    3. What configuration do you need (half duplex or full duplex) 

    4. Is there any other protection requirement that needs to be met besides IEC 61000 4-6?

    5. Is there any special feature that is needed by RS-485 (if you are unsure- you most likely just need standard RS-485; some common features include but are not limited to slew rate control, separate I/O logic supply (for 1.8V MCUs), integrated termination resistors, auto-direction, auto-polarity correction, etc...)  

    Please let me know so I can see what the best solutions we have to help meet your design goal. 

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Intellectual 585 points

    My RJ-45 port has an integrated magnet inside. Does it help we removing common mode interferences per IEC 61000-4-6? 

  • +1 in reply to Kaveh Mohammad
    TI__Guru 52382 points

    Hi Kaveh,

    Yes generally RJ-45 ports with integrated magnetics will help improve shielding the port from EMI - including common mode - but that alone may not be enough; however, it should add some benefit to the system still. 

    Please let me know if you have any other questions and I will see what I can do!

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Intellectual 585 points

    How can I know the magnet inside my RJ45 provides enough protection or I still need to add another filter? 

  • +1 in reply to Kaveh Mohammad
    TI__Guru 52382 points

    Hi Kaveh,

    Officially speaking - we don't know 100% if that would be enough as we don't test this standard as I stated in my first reply - so I wouldn't advise to say "that is enough" because there are multiple variables involved here and we don't directly test our parts on this standard.

    With that in mind I wouldn't commit to anything until you test the full system- the RJ45 may be enough on its own - in general adding more common mode filtering is safer - and I'd advise a test board with at least the option to place the filtering components. If during testing you find that you don't need the additional components then that is great - but I can't guarantee the device performance here as it isn't something we directly test. 

    Best,

    Parker Dodson