Electronics > Microcontrollers

RJ45 with integrated magnetics - different configurations

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hedley:
My company spent months trying to resolve the following issue - 10/100 ethernet worked fine on our new board . When we connected to POE or POE + ,  the link became unreliable after 50 meters of cat5e cable between edge device and POE switch . On board we have a WE 749012011 POE lan transformer . After 6 months of head scratching , pcb layout changes , specking to Wurth locally and in Germany ,  we had a response from an WE- FAE in Japan - " just flip the transformer so the common mode chokes are on the PHY side , and not the lan side,  as shown in many app notes and datasheets - Problem solved and we have 1000's of units in the field BUT I have no idea why it worked.

peter-h:
You must have been using an RJ45 without integrated magnetics.

Nominal Animal:

--- Quote from: hedley on November 24, 2022, 01:55:13 pm ---we had a response from an WE- FAE in Japan - " just flip the transformer so the common mode chokes are on the PHY side , and not the lan side,  as shown in many app notes and datasheets
--- End quote ---
Würth's own datasheet (from e.g. mouser.fi) does show the chokes on the PHY side, though.


--- Quote from: peter-h on November 24, 2022, 02:12:46 pm ---You must have been using an RJ45 without integrated magnetics.

--- End quote ---
Sure, but it does illustrate why integrated magnetics are a good thing: one less thing to worry about.

There are, in fact, RJ45 female connectors with integrated magnetics and POE taps, for example Abracon ARJM11xx-114 for 100Base-T and POE+.  Mouser has these in stock for under 3.5€ apiece, and they cost less than the Würth transformer above (at Mouser at least); both having similar current capability (600-720 mA).  I have no idea about the quality or reliability, though, just pointing them out.

peter-h:
Wurth stuff (German i.e. chinese) is extremely expensive. I doubt anybody uses it in production. Chinese e.g. Hanrun are 1/4 of the price, and then you get counterfeit Hanrun which are half the Hanrun price (but work just fine).

The Abracon ARJM11A1-009-NN-EW2 (£1.61 at Mouser, 1k+) is about 2x the price of a Hanrun HR911105 one which has an identical circuit; that's perhaps the most common non-POE layout around.

These will get blown up by a cheap chinese POE power injector.

The Abracon ARJM11D7-114-AB-EW2 (£1.74 at Mouser, 1k+) should not get blown up.

Personally I would not use Wurth or Abracon due to the price. Both are chinese and rebadged while lifting the buy price about 4x :)

Ice-Tea:
Wuerth is expensive but especially so if odering through Farnell or other distris. If you have a decent project and contact them they discount deeply. Obviously not as deep as the chinese but, well, you get what you pay for.

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