Can I use GND instead of CGND or AGND

Hello everyone, I am using this forum a lot these days :slight_smile: . I have another question. I am making PCB design with RP2040 and W5500 (First PCB design with chips). The RP2040 chip itself doesn't have AGND. I know the digital gnd is much more noiser that analog agnd. In real design (i couldn't do it yet) which one should I fallow ? I wanted to ask because I have no experience with either (GND or AGND ) .
Screen Shot 2021-10-26 at 16.44.25

1-)For example can I connected GHs_GND and CH_GND1 pins to GND instead of CGND? If I connect what will happen?( Will PCB work?)

Screen Shot 2021-10-27 at 10.07.14

In this design they connected. They are using ETH-POE, I am using RJ45 (HR91105A) are they different?

2-) I am using stepper motor driver but I willingly connect signal's pin and 5V to PCB. I will give power motor driver from another adapter (Switch mode adapter.) Will it be a problem if I use GND again?
Thank you.

3-) This question is off topic but does footprint matter when choosing a crystal (4-SMD or HC-49/US)? W5500 doesn't give crystal name so I am choosing. Does crystal matter I mean If I choose same frequency and calculate right capacitor for it, It will work right? Thank you.

I think that it's up to you to provide separate GND lanes for analog, digital (and protective) ground. CH_GND1/2 suggests to me that the channels can be used in differential or 4-wire sensor mode.

The motor power supply should only be connected to the driver chip
so that motor current can not flow over digital ground wires.

The AGND and AVCC pins on the W5500 are for the ethernet drivers and/or receive amps I think. Make sure the analog supply is separated from the digital with a suitable ferrite bead(s) to keep high frequency noise from it - AVdd needs good decoupling according to the reference schematic.

Reference schematic for W55000:
https://wizwiki.net/wiki/doku.php/products:w5500:refschematic

Yes I am doing this schematic. They are using 1nF/2kV capacitor for separate GND and CGND.I was thinking I don't need 1nF/2kV but now I will use it. I am doing same decoupling except I am not using 10uF/16V tantalum capacitor, I am using 10uF/25 or 10uF/50 ceramic capacitor.

Thank you.

That's for lightning/transient protection on the ethernet side of the transformers. I think the idea is that transient common-mode voltage spikes induced on the CAT5 cable get shorted out by the capacitor before the tiny pulse transformers in the magnetics block arc over!

Hmm, okay I got it. I am using like this in my design. MH1608-121 has 100 ohm DCR and 120 ohm Impedance.
Screen Shot 2021-10-27 at 13.45.29

My 3.3V is coming from here

MarkT, you helped me a lot thank you. Should I use that CGND thing or can I just connect GND.

CGND is external, the other side of the ethernet isolation barrier, it must never be connected to your circuit directly or you lose the isolation barrier (which for instance would blow something up if you used PoE.) Ethernet connections are transformer isolated to avoid all the issues of ground loops (and coincidentally allowing PoE to exist).

Okay MarkT thank you. I didn't pcb design with CGND but I found 1 design. On this design he/she used CGND but he/she connected CGND to AGND polygon on PCB design side.
I will use AGND polygon for CGND little square left bottom side ( Rest will be GND polygon.) That is how I do it probably. As I said PR2040 don't have AGND will it be a problem?

The ethernet chip requires a clean analog supply, nothing to do with the rest of the board.

Ethernet signals attenuate rapidly with distance, so for long cable runs the ethernet receivers have to handle millivolt signal levels which is why a good analog supply is required. If you don't have long cable runs you can be sloppy about this.

Okay ,thank you. For a clean analog supply, I am using a ferrite bead.