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Hardware PCB LAN8720A Problems

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Jan 18, 2021
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I have designed and assembled a board that uses LAN8720A and ESP32 to create a POE setup. I broke it up into 3 sections for testing and verification; uC w/PHY, POE PD Controller.

But i test without POE in this case I'm currently only testing the uC/PHY isolated from everything else and providing power through USB dropping down to 3.3 using a linear reg. !!

The LAN8720A has communication with the esp32 but not with the network. i.e. the phy is configured without error and even detects when the LAN cable is connected and disconnected but it never gets an IP address and/or connect to MQTT server !!

I have a waveshare breakout board for the LAN8720A for which I followed sautter's guide and it works well. ... ng-lan8720

I used the waveshare schematic as my starting point ... ematic.pdf

When I compare schematics I don't see anything glaring that would seem to indicate improper connection so my guess is my issue is with layout.

i use transformers inside an RJ45 jack :

i have 4 layer pcb stackup 1.6mm (signal-GND-POWER-SIGNAL) with Impedance checked construction with EasyEDA : impedence diff 100R :

-track space 4.70 mil-track with 6.00 mil-track height 1.36 mil
-isolation heigth 7.08 mil
-dielectic cst FR4 4.300


Let me know if you see anything in the schematic or layout that might an issue.

Patiently waiting for your input.


I understand your report so, that managment interface is working, but RMII not. Hope you can verify that the ESP32 side of RMII is configure correctly.

The REFCLK wiring looks incorrect (also in the waveshare schematic). If XTAL input is driven by 50 MHz clock (nINTSEL = 1 configuration), nINT/REFCLKO is an active low interrupt output and should not connect to REFCLK line, R20 must be omitted. You however don't show the actual configuration pinstraps of your circuit.

Apart from this possible issue, most likely reason for circuit failure is solder problem of the small 8720 package.

hi @FvM, for first thanks for ur replay ,

1-so about sof in esp32 its done correctly bcs i tested with LAN8720A breakout and its work well .
2-i have resistor 4.7k to vcc and capacitor 100n to gnd for nINTSEL .
3- nINT/REFCLKO ur right should not connect to REFCLK is i see datasheet , but in schematic of breakout LAN8720A is connected that why i put it

and waveshare for 50mhz i think i can adjust termination resistors for better adaptation ,now i use 0R but i will try with value 33R to 50R i think this can solve problem .

and other thing about signal TXP,TXN and RXP, RXN i think i did it good with differential pair routing with impedance diff 100R

but i dont now why i didn't do same thing with RXD[0:1] and TXD[0:1] and i routed them normal :( i think i should routed them like RX and TX using differential pair routing with impedance diff 100R




--- Updated ---

and as u can see TDX[1] i use via and bottom piste too :eek: but for prototype i think it should work, just i will change them for final board


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RMII lines are single ended signals, not differential pairs. I won't expect any signal quality problems if they are routed over a continuous ground plane.

Regarding REFCLK wiring, you should decide if you follow 8720 datasheet or dubious sources.

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