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DP83848-HT: Problems with using the Bob Smith Terminationi(Center Tap of transformer to 75 ohm resistor and cap) during Lightning Pin Injection testing

Part Number: DP83848-HT


I was looking at your Data Sheet for the 83848 and it recommends using the Bob Smith Termination.  Seems like all manufacturers do.  But during Lightning Pin injection testing we burned up one of these resistors.   I was wondering why this termination is recommended since I'm starting to see many articles suggesting that this termination is not necessary.  

What gains do we see from this type of termination over using nothing at all?   If we use nothing do you think we would see more noise at the Phy?


Mike Davis

BAE Systems.

  • Mike,
    Let me follow up with the experts in the commercial team and provide some feedback shortly.

  • Mike, here is feedback from the experts. It is inline with your comments.
    This is a hot topic for debate, as Mike points out many articles are written around this. School of thought is the Bob Smith termination is not necessary when using a CMC, and doesn’t have much impact when used with a CMC. Couple that with the point that common mode noise is really an emissions problem, and some designs can give up emissions to see better immunity, there may be times where Bob Smith can be removed.
    Hopefully this is helpful.

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