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DP83867 - Do the SGMII_SIP and SGMII_SIN pins require an external 100 ohm differential termination resistor?

David Sandler
Intellectual 1910 points

Hi,

For DP83867 do the SGMII_SIP and SGMII_SIN pins require an external 100 ohm differential termination resistor?  

In table 2, note 1 says that internal pull-up and pull down resistors are disabled when the device enters functional mode.  Section 7.1 says I should pull all unused inputs up or down.  What is the point of pull-up and pull down resistors on non-strap input pins, such s TX_D3, if they go away after the device enters functional mode?   Are they really disabled?

 

Also,

Besides a reduction in power, is there any advantage to using an external 1.8V supply with this device.  

Regards,

David

  • 0
    TI__Mastermind 18425 points

    Hi David,

    The SGMII SIP and SIN pins do not need external 100 ohm resistor. The PCB traces for the SGMII signals should be differentially routed with 100ohm differential resistance.

    Strap pins are sampled on power up and hard reset. With the help of strap resistors, a desired voltage can be set on these pins so that on power-up/reset the PHY enters the desired mode (1,2,3 or 4). Internal resistors are included so that the pins will always have a default voltage should the user decides to leave these pins unconnected. After the device enters functional mode, these resistor are not used in normal PHY operation. Effectively, they are disabled.

    Strap pins on shared signal lines can be pulled in an unwanted mode if there are any stray resistances on those signal lines. This is why externally strapping the pins is recommended. Non-strap pins which are not connected anywhere else can be left floating.

     

    Lastly, the 1.8V triple supply mode is only used for configuring the PHY in low power mode. Other than that, the PHY functionality will not change between dual and triple supply mode.

    -Regards,

    Aniruddha