I am adding Power over Ethernet
functionality in my Toradex's
System-on-module (Colibri iMX6ULL) based carrier-board design. I am having confusion in selecting the MagJack
for the design. I want to implement Mode A
and Mode B
. However, It would be great if someone can comment on the designs for 4-pair mode
.
The MagJack that I am considering is SI-52003-F. The schematics presented in their datasheet has been posted below:
Since, the schematics shows center-tap on network side of the transformer and the Power Pins are brought out. I think it will work for my application but I am not 100% sure. The rectification designs that I am considering are given below:
Design 1 is simplest and requires less space and components. It assumes the pinout and polarity as given on wikipedia.
Design 2 assumes the polarity can be different and makes sure non-IEEE 802.3af PSE works with my PCB.
My earlier version of the PCB (without PoE) has a MagJack (without centre-tap transformer). The Ethernet part of the schematics is below: (R19 is unassembled)
My questions are:
- What would be best Design (1 or 2) for my application?
- The MagJack that I have been considering, Is it suitable for PoE (Mode A and Mode B both)?
- The last question could be a stupid question but still I want to be sure before proceeding further. I was using this MagJack in earlier version of my PCB and it was working perfectly. However, I am moving with SI-52003-f Magjack for PoE capabilities. Will it make any difference for the Ethernet Controller if I switch the MagJack?
Best Answer
Design 2 gives your system more tolerance for miswiring, which is a good thing. These days it's generally not necessary to pay attention to whether wiring is straight-through or crossed over, because with widely available gigabit and auto-MDI/X the hardware just figures it out. Design 2 will be similarly tolerant, and will work even if pairs are crossed over or otherwise mixed up.
It appears to be designed to support PoE, given the way the center taps and extra pairs are brought out and labeled in the schematic.
No, it won't make any difference. Ethernet magnetics are all pretty much designed to do the same thing, and the PHY will be designed to tolerate a wide range of cabling characteristics anyway, so the magnetics will make little difference by comparison.