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Hot!Ethernet Troubleshooting

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Jim Nickerson
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Re: Ethernet Troubleshooting 2018/02/20 16:37:13 (permalink)
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post to try to fix blinking on page 3
edit: and it works, no more blinking
#41
muellernick
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Re: Ethernet Troubleshooting 2018/02/21 07:07:42 (permalink)
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I have a board with the LAN8740A, don't know about differences to the LAN8720A. I'm using MII.
I have posted the schematic here about 1 to 2 weeks ago, maybe that helps.
 
Are you sure that you used the same RJ45 (with integrated magnetics)? There are so many variants, it can be confusing (at least for me).
 
For the supply voltage, I can measure a bunch here if you want.
Until now, only one board was DOA in regard to ETH. But the reason was visible: A big blob of solder.
 
Feel free to ask, if my LAN8740A is of any help.
 
Nick
#42
friesen
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Re: Ethernet Troubleshooting 2018/02/22 07:12:55 (permalink)
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@matta, I have tried to understand your last post, It isn't very clear.

Erik Friesen
#43
matta
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Re: Ethernet Troubleshooting 2018/02/22 07:35:36 (permalink)
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Apologies, I think I did a poor job of explaining.
 
To summarize previous posts, I had a working implementation of ethernet on a PCB that I assembled myself. I then had some assembled professionally and when they came back they didn't work (never auto negotiated, didn't respond when ethernet cable was plugged in).
 
As it turns out, I made a mistake when I assembled the first one and had a bad solder joint on one of the 50 Ohm termination resistors to Vdda. It just so happens that this is what made it work while the others do not. When I take off all the 50 Ohm Terminators and replace them with 100 Ohm everything works as expected on all boards. Now I just need to figure out why that is the case, since I am sure it is some other thing I have done wrong.
#44
mattgarfield
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Re: Ethernet Troubleshooting 2019/04/01 11:33:15 (permalink)
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@matta - any follow up to your experimental success with swapping the terminating resistors from 50Ω to 100Ω? Did you nail down the root cause of why this seemed to help your design?
 
My ETH PHY communication issues aren't as extreme as what you described, but I am having some intermittent communication problems that seem to be HW related and I'm trying to build a list of topics to dive deeper into.
 
I designed a product that uses PIC32MZ2048EFM064 with LAN8740AI and based my layout on the Microchip Dev board DM990004. I've manufactured about 500 units and roughly 15% (across lots and CMs) seem to experience a higher rate of Ethernet communication errors. I'm trying to figure out if maybe my design is operating on the edge of the ideal range and maybe some variability in tolerance of passives are pushing some devices over the line. 
#45
matta
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Re: Ethernet Troubleshooting 2019/04/01 12:56:22 (permalink)
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Not completely... I cleaned up the layout taking care to follow the example layouts more precisely and being more diligent with my decouping capacitor layout. The new revision works with the typical 50 ohm terminators. I think most of my problems came from my assemblers not getting the LAN8740A down correctly. It was a on a PCB with thicker metal and I'm not sure they gave it enough time. I realize this doesn't explain why switching to 100 ohm terminators worked, but schedule dictated I give up on figuring that out.
#46
mattgarfield
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Re: Ethernet Troubleshooting 2019/04/01 14:43:43 (permalink)
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Understandable. With so many variables at play, there's no guarantee for a conclusive reason why one thing works over another. It's helpful to know that your setup is working with the recommended 50 Ω termination resistors now though. That's enough to satisfy me that I probably shouldn't worry about hunting this thread down either. Thanks!
#47
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