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DP83848K: Compliance with the ETHERNET standard in reference design TIDA-00207.

Part Number: DP83848K
Other Parts Discussed in Thread: TIDA-00207

According to the ETHERNET standard, clause 8.3.2.1.
Isolation shall  withstand at least one of the following electrical strength tests:

a) 1500 V rms at 50 Hz to 60 Hz for 60 s, applied as specified in 5.3.2 of IEC 60950: 1991.

b) 2250 Vdc for 60 s, applied as specified in 5.3.2 of IEC 60950: 1991.

If you refer to the standard for PCBs IPC-2221A, Table 6-1. There are recommendations on the gaps between the conductors on the printed circuit board. For convenience of calculation, I used the program Saturn PCB.

As you can see, the minimum clearance should be 3.85mm! However, on the printed circuit board in the reference design TIDA-00207, such a gap is not observed. Here is an example from an open pcb file:

How would you comment on this? This is my fault or yours?

Thanks in advance for the answer!

  • Hi Andrey,

    The microstrip trace (Red) is on the top layer and the ground plane is on the Layer 2. Their edge to edge distance is 35mil but the vertical distance will also come into play here since they are on different layers. It looks like the PCB tool assumes that one conductor is right on top of the other conductor which is not the case here. Also the voltage test is 1500Vrms at 50Hz-60Hz for 60s, it is not clear if the calculation tool takes this into consideration.

    Lastly, the isolation requirement is generally applied to the magnetics used in Ethernet applications. Magnetics manufacturers will often list in their datasheets that their devices are tested for the above spec. From a layout perspective we recommend customers to keep the area below the magnetics void and to keep the earth ground physically seperated from signal traces as much as possible. I hope this helps answer your question.

    -Regards,
    Aniruddha