Using Wiznet chips alongside PoE solution

Question

Hello, I am updating a prototype design. The original prototype uses the Wiz820io. My question concerns options for removing the need for the rather large RJ45 connector and “ethernet fly wire” as I call it. My device is powered via PoE and to the best of my knowledge the designer has enabled variants A and B which means power can come in on dedicated pins or it can be “phantom power” on the data lines. Attached is the relevant portions of the schematic. PoE908×627 9.25 KB So you can see the data lines, after being transformed once for use in the PoE system go into an RJ45 header. Not pictured is that this header has a short ethernet cable (“ethernet fly wire”) that runs into the RJ45 connector that is part of the Wiz820io. Now, what I want to do is just put the W5200 (or suitable variant) down onto my main board. I was thinking that i could actually just run the data lines after my transformer directly into the W5200 but after floating around these forums it seems a 3.3V connection is necessary to the center taps of the transfomer. Would that be RCT and TCT on my schematic? Perhaps I am mistaken and the built in transformer of the Wiz820io is totally necessary? I’m afraid I don’t have really poignant questions here. I’m a beginner to this embedded ethernet world. Does anyone have any insights into using W5200 (or variants) within PoE devices which can receive power over the data lines and thus have the external transformer configuration that I have here? To repeat my main goal. I want to drop the Wiz820io and lay down the W5200 (or variant) without the built in RJ45 and transformer. What am I missing in order to accomplish this goal?

scott · Answer

Dear @JWizard I can’t see well because the picture you attached is blurred, and I can’t understand your current status accurately. All I understand is, You used a short Ethernet cable from J2 to connect to WIZ820io. You want to remove WIZ820io from the circuit diagram and use W5200. Is that right? If so, you can connect the MDI (Ethernet) signal from the W5200 to your transformer. Your current form is a two-pass Transformer input/output MDI signal, but you can do it with one Transformers. You must connect 3.3V to the RCT and TCT. Thank you. Scott