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DP83TG720S-Q1: 1000Base-T1 Grounding necessity

Santhoshwaran Govindaraj
Prodigy 140 points
Part Number: DP83TG720S-Q1

Tool/software:

Hi,

In our project, we are using the DP83TG720S-Q1. There will not be any ground pin in the MDI signal connector only shield ground will presented.

We have connected the connector shield pin to the shield connector, and the shield is connected to our board Ground through a 1M ohm resistor and capacitor, as shown in the image below.

Is this correct?

We are also curious about the necessity of a ground for the return path of the differential pair. Unlike USB, it does not require a ground, does it?



  • 0
    TI__Genius 14006 points

    Hi Santoshwaran,

    If you want to have GND separation in your design for EMC purposes, you should include the CM termination circuit as part of your connector ground (CONN_GND).

    See the example below, the CM termination (1k res, 100k res, and 4700 pF cap) shares the same GND as the connector, but a different GND from the rest of the board.

    We recommend a 0 ohm resistor and 4.7nF isolation capacitor (capacitor is depopulated) to separate board GND from connector GND.

    If you want to maximize EMC performance, you can add 1-2 additional resistors and use a larger SMD packaging size (0805+).

    Best regards,

    Melissa

  • 0 in reply to Melissa Chang
    Prodigy 140 points

    Hi Melissa,

    Since you mentioned connecting Zero Ohms, does that mean the ground is optional, Unlike in the data differential pairs in USB?

  • 0 in reply to Santhoshwaran Govindaraj
    TI__Genius 14006 points

    Hi Santoshwaran,

    The GND separation is optional, yes. If you have strict EMC requirements, you should use the GND separation.

    Best regards,

    Melissa