DP83867IR: Capacitive coupling of the magnetics?

reto hermann

Part Number: DP83867IR

Hello,

on a custom board we plan to to use the DP83867. Unfortunately, the magnetics are located on another, existing board that can't be changed. That board was designed for a PHY with current mode line drivers and the center taps of the magnetics are pulled to 3.3V. My concern is now that this does not work in combination with the voltage mode line drivers of the DP83867.

Is it possible to decouple the line drivers from the 3.3V bias voltage using capacitors? The complete circuit would then look like this:

My second question: Are there GBE PHYs with current mode line drivers?

Thank you for your reply!

Best regards
Reto

over 3 years ago

0 Hillman Lin over 3 years ago

TI__Mastermind 25955 points

Hi Reto,

No, DP83867 is a voltage mode driver. The center tap cannot be shorted as given in the datasheet in the figure 31.

Sincerely,

Hillman Lin

0 reto hermann over 3 years ago in reply to Hillman Lin

Intellectual 720 points

Hi,

thank you for your quick reply! Are there GBE PHYs with current mode line drivers from TI?

Best regards

0 Hillman Lin over 3 years ago in reply to reto hermann

TI__Mastermind 25955 points

Hi Reto,

We don't have any GBE PHYs that support the current line driver.

Sincerely,

Hillman Lin

0 reto hermann over 3 years ago in reply to Hillman Lin

Intellectual 720 points

Hello Hillman,

thank you for your answer. In your first answer you wrote that the center taps of the magnetics must not be connected with each other but in this reference design https://www.ti.com/tool/SK-AM62 they use an Ethernet connector with intergrated magnetics and that connector shorts the center taps internally and this setup appears to work.

Best regards
Reto

0 Hillman Lin over 3 years ago in reply to reto hermann

TI__Mastermind 25955 points

Hi Reto,

Center taps need to be shorted through caps as the picture shown below. Please do follow the datasheet recommendation for MDI connection.

Regards,

Hillman Lin

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DP83867IR: Capacitive coupling of the magnetics?