WIZnet Developer Forum

W5500 PCB Layout help/advice

Hello, I am working on a project that includes the W5500 circuit, this is the first time i had the opportunity to layout Ethernet Interface circuits.

My questions are :

  1. Does the differential pair impedance 100 ohm for the pair and 50 ohm for the individual signals matter if the traces are very short and crowded with termination resistors and other components as shown in the schematic below ? if yes, which part exactly should i implement ( before / after the 33 ohm or after the TVS diode if that is any different.

  2. I am aware of the HW Guide line ( check useful notes, point number 2 ) but in order to implement proper impedance on a 2 layer board then it is going to be unsuitable for the entire board 20 x 10 cm . This W5500 Ethernet shield here has eagle source files, i checked it and as far as i understand it may not follow strict impedance control guidelines ( maybe things are a bit forgiving ? ).

  3. I have added TVS diodes (IC2, IC4) [(USBLC6-2SC6)] in the differential pair path as shown in the schematics below, any notes on the selection of this unit or any notes on the layout would be very much appreciated.

  4. As shown in the layout screenshot below, I made a separation on top layer (red) between the differential pair and the ground plane. and left the bottom ground plane as clear as i can get for now, any suggestions or comments are welcome.

  5. Under the TVS diode at the differential pair path, i needed to connect a 3.3V and that line is under the IC, i’ve attached a picture to further explain my question, is this a real problem or not ?.

  6. Does the center tap connections need to have any impedance controlled value ?

  7. This may be off topic , but any ideas on how to connect the RJ45 Metal shield to the ground plane , the board will be enclosed in a metal box, how can i connect them ( System ground ----- RJ45 Metal Chassis ------ Metal Enclosure ).

Some useful notes :

  1. I am using this RJ45 Straight Connector MFG Part no. 74990101210 from Wurth Electronics.

  2. I found this Wiznet Wiki HW Guidelines page to do the layout here

  3. The trace width of the differential pair is 10 mils and the distance between the pair is 10 mils.

Note: I had to put all images in one high resolution image ( upload limit ).

I would appreciate any feedback. Thanks in advance !

Regards
Sultan

Don’t know much about PCB layout. However, shouldn’t pin #23 RSVD be tied to ground?

I checked the reference schematic and the schematic of the w5500 ethernet shield which wiznet sells, both left it not connected. According to the datasheet, it needs to be tied to ground, i’ll update it then. Thanks for the note.

please help …

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