Schematic Design question

Question

Hi and many thanks for taking the time to read this post. As this Is my first design, I wanted to be sure that I didn’t do anythings wrong before trying to make any PCB design. Basics function of the board : It’s an ethernet module based on the W5100 chip with PoE capabilities using a PEM1203 module. I do have a few question regarding the official “Layout guide” of the W5100 and the “Reference schematics REV 2.1”. On the reference schematics, difference ground are used with a MAG-JACK RJ45 connector. But on the “Layout guide” the magnetics are separated from the RJ45 connector with an isolation area. Is this possible to achieve with internals magnetics? (such as HY931147C RJ45 connector). Also, in the “Layout guide” it’s said : “It is better that do not try to partition GND at all.” So now I’m really confused… Do I need then to have Analog / Digital / chassis ground then ? or can I just connect all of the different ground to the same plain? And finally, On the “reference schematic” Analog / digital ground are connected with inductor FB1 but no values are given. What value do you recommend for that component? Thanks you a lot Edit : I forgot the bypass caps. I just updated the Schematic. Schematic_Ethernet-shield-PoE_Ethernet-shielt-W5100-PoE-Arduino-mini_20180615123939.pdf (68,5 Ko) Schematic_Ethernet-shield-PoE_Ethernet-shielt-W5100-PoE-Arduino-mini_20180615123939.pdf (68,5 Ko)

Eugeny · Answer

All questions are really on spot. dezmob: Is this possible to achieve with internals magnetics? No, then only thing you may do in this case is not placing ground plane under the MagJack. I researched the matters and decided that for hobbyist projects this measurement is too much. Professional projects use external magnetics anyway, which can have grounds properly separated. dezmob: It is better that do not try to partition GND at all Do not partition digital and analog grounds (even with ferrite bead), but partition 3V3D and 3V3A with ferrite bead - this should be enough. In any case you must ensure your power source is clean at digital side. dezmob: FB1 but no values are given. I have taken arbitrary value of 30. Probably took this value from Arduino Eth Shield design

dezmob · Answer

Thanks you very much for taking the time to help me. Im a bit confused: Do not partition digital and analog grounds (even with ferrite bead) and then but partition 3V3D and 3V3A with ferrite bead So basically both 3V3D ans 3V3A will be connected to the same ground plain if I understand it correctly? I have taken arbitrary value of 30. Probably took this value from Arduino Eth Shield design So no need for me to bother with FB1 since I don’t need to partition GND and GNDA right? I’ve connected all the GND to the same plain even the chassis GND I don’t know if I still need to make different plain for those two. I’ve looked up the EtherTen from Freetronics and it doesn’t seems that they use different GND for the chassis. I’ll start the PCB and come back at you with the layout, I would really appreciate any feedback, tips, you seems to have a lot of experience of this chip according to your many post. here’s my schematics for now, let me know if you see something horribly wrong Thanks you very much! Schematic_Ethernet-shield-with-PoE-Mode-A-B-for-Arduino-Pro-Mini-3.3V_Ethernet-shielt-W5100-PoE-Arduino-mini_20180620083129.pdf (68,2 Ko)

dezmob · Answer

Eugeny: I recommend you perform prototyping first becore making big batch of the devices. Ok don’t worry, I won’t make any expensive mistakes, this is just for the fun of it, and learning in the process