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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:

enter image description here

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:

enter image description here

Design 1 is simplest and requires less space and components. It assumes the pinout and polarity as given on wikipedia.

enter image description here

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)

enter image description here

My questions are:

  1. What would be best Design (1 or 2) for my application?
  2. The MagJack that I have been considering, Is it suitable for PoE (Mode A and Mode B both)?
  3. 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?
abhiarora
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1 Answers1

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What would be best Design (1 or 2) for my application?

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.

The MagJack that I have been considering, Is it suitable for PoE (Mode A and Mode B both)?

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.

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?

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.

ajb
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