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Question about DP83865 twsted pair impedance

Go
Genius 4220 points
Other Parts Discussed in Thread: DP83865

Hi,

I'd like ask about DP83865(Giga Ether Phy) as follows,

In DP83865 D/S page66 5.7 Twisted Pair Interface,
There is some description about the twisted pair impedance as follows,

"50-Ohm controlled impedance with respect to VDD or GND"

While in the SNLA056D App note"DP83865 Gig PHYTER V 10/100/1000 Ethernet Physical Layer Design Guide"
page10 8 Twisted Pair Interface,

There is some description about the twisted pair impedance as well,
but the expression is silghtly different from that of in DP83865 D/S page66.

"50-Ohm controlled impedance with respect to AVDD"

which one is correct?

Thanks

Go

  • 0
    TI__Mastermind 31600 points

    The Media Dependent Interface (MDI), also referred to as the Twisted Pair Interface (TPI), is biased from a 2.5V analog voltage supply.  This supply may be referred to as the Analog VDD (AVDD).  It is acceptable for the MDI traces to have a 50 Ohm characteristic impedance relative to either this 2.5V analog supply or to ground.  The most common approach is to reference ground.

    Patrick