The paired MDI signals from the PHY to the magnetics in a GbE application are each terminated by a 50R resistor and then together to a 10nF capacitor to GND. However some applications connect the 2 resistors to Vcc (2.5V) as well. Can anyone explain why some configurations are like this and others aren't? Is it something specific to the magnetics?
TIA,
Rog.
It is not the magnetics; more likely, some implementations need a "pullup" to the higher voltage to provide power to the output driver through the terminating resistors. This is a function of the configuration of the output transistors in the PHY chip.
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