I am confused as to the preferred placement of Ethernet PHY and magnetics. I thought that in general, the closer the better. But then SMSC/Microchip app note (http://ww1.microchip.com/downloads/en/AppNotes/en562744.pdf) says:
SMSC recommends a distance between the LAN950x and the magnetics of 1.0” at a minimum and 3.0” at a maximum.
Confusingly enough, earlier in the same paragraph one can read:
Ideally, the LAN device should then be placed as close as possible to the magnetics.
I used the excellent LANcheck service from Microchip and the expert reviewing my design also suggested that a minimum of 1" separation between the chip and magnetics is suggested to minimize EMI.
I do not understand why increasing the distance the signals have to travel would ever minimize EMI?
Also, a related question — I do not understand reasons for the following:
To maximize ESD performance, the designer should consider selecting a discrete transformer as opposed to an integrated magnetic/RJ45 module. This may simplify routing and allow greater separation in the Ethernet front end to enhance ESD/susceptibility performance.
Intuitively, magnetics that are embedded inside a shielded RJ45 module should be a better solution than discrete components with traces inbetween?
So, to summarize:
- should I try to maintain a minimum distance between the PHY and magnetics or should they be placed as close as possible?
- is it better to use a "magjack" or separate magnetics and RJ45 jack?