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DP83867IS: Termination Resistors for Rx_D0...etc

Darren (FAE)
Expert 5483 points
Part Number: DP83867IS
Other Parts Discussed in Thread: DP83867IR

The datasheet for the DP83867IS says there are internal termination resistors for the transmission lines...

Some reference designs for the DP83867IR show 0Ω resistors on the transmission lines, because of this.

http://www.ti.com/tool/TIDA-010010

http://www.ti.com/tool/TIDA-00204

However, in the TMDX654GPEVM, the PHY has 22Ω termination resistors on Tx/Rx lines...(see below image)

http://www.ti.com/tool/TMDX654GPEVM

What happens if termination resistance is used? Could this cause issues somehow with the internal termination? Is there a reason why you would still want external termination? 

  • 0
    TI__Expert 7040 points

    Hi Darren,

    The external series termination is not necessary for the DP83867IS, due to the internal 50 ohm series resistance. Additional external termination can be used balance trace impedance mismatch or dampen MAC signals. 

    Register 0x0170 also provides this option by controlling the internal series resistance on these pins.

    Regards,
    Justin