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DP83867E: Transformer center tap connection

Jeff Ross
Prodigy 90 points
Part Number: DP83867E

We will be using the DP83876E transceiver in a new design and connected to an RJ45 with integrated magnetics (Pulse JXD0-0002NL-X1).

I'm unclear about the center tap connection of the transformer, whether it should be capacitively coupled to ground per the datasheet or to a voltage rail. Our previous designs have used transceivers from other manufacturers, and in all of them the transform center tap connection is typically made to the Vdd-IO of the device with some additional power filtering.

I'm not a magnetics guy but can see that the transformer configuration in your reference design (Pulse HX5008NL) is different than in the Pulse JXD0-0002NL-X1.

From what I can gather, your DP83876E transceiver does not requiring the center tap biasing, but since I'm unclear I'm hoping for some expert advice.

Thanks

Jeff Ross

  • 0
    TI__Mastermind 18425 points
    Hi Jeff,

    For DP83867, all 4 center taps of the transformer should be individually coupled to ground via 4 separate capacitors. The center taps do not need to be pulled to any voltage. We do not recommend tying the center taps of the transformer together as shown in the datasheet for JXD0-0002NL-X1.

    As for the difference between coupling schemes of the previous PHYs and DP83867, it is related to the line driver implemented in the PHY.

    -Regards,
    Aniruddha