I have Ethernet PHY from Marvell (88E1111-B2-BAB1I000) and Ethernet transformer (S558-5999-AT-F). By mistake the MDI P&N connection got interchanged on the transformer side. Will it work?
Electronic – Connecting Transformer to Ethernet PHY
ethernettransformer
Related Solutions
- Where is the transformer? How exactly the termination is done, and what impedance it needs to be is a function of the PHY's requirements, which then dictate a particular transformer configuration. Since the transformer is integral to termination, we need to see it. You should really show everything from the PHY all the way to the RJ-45 jack.
Your terminations look correct assuming this PHY requires transformers with 1:1 ratio.
- Do you really need to terminate all 4 pairs? Ethernet data is carried on RJ-45 pins 1,2 and 3,6. The other two pair aren't used for data but could be used for POE. If you intend to use POE then you definitely don't want the 100 Ω between pairs. If not, just leave them floating. Why are they connected to the PHY at all? Exactly what type of ethernet are you implementing here?
- I really don't like disconnecting the PHY ground and main ground with a inductor, as you do with L9. I can understand you want to keep the PHY's high frequency power/ground current off the main ground plane. It looks like you have isolated the PHY's power nicely with L10 and bypass caps C69-C74. All you need to do is connect all the PHY grounds together, then make sure that net has exactly one connection to the main ground. That keeps the nasty high frequency loop currents local, but still gives the PHY the same 0V reference as the rest of the board. With the inductor separating the grounds, the PHY essentially won't have the same 0V reference as the rest of the circuit at high frequencies. That's not what you want.
No, that jack is not a Magjack. It is a bare connector. I say that because the chip next to it is the Bel S558-5999-46. It's specific datasheet is here. It is an Ethernet 10/100Base-T Lan Magnetic Single Port Transformer. You could use that. Or both the chip and the jack. It should be compatible with the ENC28J60, most common 10/100 magnetic transformer would. The S558-5999-46 is a 1:1 Ratio transformer. See the schematic below for tappings and pinout.
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Best Answer
The 88E1111 Product Brief (which is the only interesting document I found), says "Automatic polarity correction" in the features. So it seems you're fine. However, they don't mention it later on, so we don't know how it works and if there are restrictions.
Overall, I wouldn't recommend lauching a 10000 production run without having made sure first, but if you are in prototyping phase, it's definitely worth a try. And if your prototype has problems, you can always make a custom RJ45 cable with flipped P/N wires to make it work.
Note it also does auto MDI/MDIX, so you could have flipped the pairs as well (just sayin').