EK-TM4C1294XL: Ethernet doesn't work in our design

Hi, 

  Is there any reason why you want to use a separate power plane for the termination resistors? The PHY interface is very sensitive to noise and transient events. I would strongly recommend the MCU and the external components for the Ethernet to have the same reference power and ground. 

  BTW, I do not see the ESD protection diode on your schematic and neither the Bob Smith termination resistors on your schematic. Without it, even the one that currently works may not work down the road due to noise and EMC. The chip may be even damaged as a result of voltage surge on the Ethernet due to noises. 

  Please refer to the TM4C129 system design guide line for best practices on Ethernet interface design. https://www.ti.com/lit/pdf/spma056

  Here is a good app note on impedance matching on the Ethernet interface. https://www.ti.com/lit/an/snla079d/snla079d.pdf?ts=1610722213390&ref_url=https%253A%252F%252Fwww.google.com%252F

  Here is another article on good Ethernet interface design. https://www.we-online.com/catalog/media/o119953v446%20Tutorials_Connecting%20LAN%20Transformers_EN%20(rev1).pdf

Hi!

The reason why I want to use separate power supplies is that microcontroller with one LDO 3.3V is located on PCB, which represents ready module and is already commonly used, but Ethernet circuit, including RJ-45 with transformers, protection (I just didn't draw it), Bob Smith, termination resistors, etc. is located on another, mezzanine board being developed now, with the second LDO, which is placed there because 3.3V from the first board is absent on the mezzanine connector (previous designer did not take it into account).

So, if it's not possible, however, to make Ethernet work with separate supplies... ok. Thanks for consultation and help!

Regards,

Svetlana