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DP83867IS: Magnetics Centre-Tap

Bernhard Boehmer
Expert 1120 points
Part Number: DP83867IS

Hello TI,

snla246a states that: "Each center tap of the magnetics should be independently de-coupled to ground via a 0.1uF capacitor". However, RJ45 connectors with integrated magnetics almost always connect the centre-taps of the integrated cores together, either directly:

or more indirectly:

and make this connection available on a single pin.

Questions:

1. Are these RJ45 connectors with integrated magnetics still useable (contrary to the first statement above), or is operation of the DP83867IS using RJ45 connectors with integrated magnetics not possible?

2. Should operation with integrated magnetics be possible, which of the two configurations above is preferred?

  • 0
    TI__Mastermind 19780 points
    Hi Bernhard,

    Integrated magnetics commonly join all the center taps as you have stated, but some options are available. For example the DP83867IRPAP EVM uses the Wurth integrated magnetics PN: 7499111000A that pin out each CT individually.

    We do not recommend center-taps joined because we have seen it affect the shaping of the auto-negotiation FLP. While it did not have an immediate impact, it was not compliant with IEEE spec and could pose a problem once going to production in high volume.

    In addition, the second schematic you show places the CMC on the PHY side of the transformer and this is not suggested for the DP83867.

    I recommend using the Wurth magnetics if you cannot find other suitable integrated jacks and use the example from the DP83867IRPAP EVM.

    Best Regards,