Hi ,

I see sometimes MDI pairs length limitations in Datasheets of components of a few inches (regarding the PCB routing length).
Why is there such a strict limitation if after that the ETHERNET cable can be 100 meters long? Will it not work correctly even if the MDI pairs length on the PCB will be 20 inch or even more ?

Thanks.

 

Transmission line theory at high frequencies is anything but intuitive. Unless you understand the mathematics and the geometry of what you are working with your speculations are probably wrong.

 

As long as you route it with controled impedance . minimum via's , clearance from other signals on the pcb - what is the difference between routing it on the PCB and the Cat 5 cable which could be 100 meters long ?