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10 years, 4 months ago.
Connecting mbed PHY to RJ45 without magnetics
Hello, people!
I'm looking for some advice on connecting mbed Ethernet PHY to a RJ45 port without using magnetics. So, the application note http://www.ti.com/lit/an/snla088a/snla088a.pdf describes how to do this by using blocking capacitors, as shows the schematics below:
/media/uploads/diegostefano/capacitive_coupling.bmp
I'm running some experiences on a breadboard and my intention is to use a CAT5 cable clipped only on one side (the side that will going to be connected to the switch), and in the other side of the cable I will conect the wires in the breadboard. Finally, I would use the circuit above to interface the mbed with my LAN. Does this make sense? Will it damage the mbed PHY somehow?
Thanks a lot in advance!
1 Answer
10 years, 4 months ago.
Diego,
If you LAN connection is extremely short (<1m) and you have no ESD issues, then you can do your cap coupling technique. Generically speaking, it is possible that some Phys may have an issue if DC biasing through the transformer is used. i.e. It is possible that the Phy may require biasing around Vdd / 2 rather than pullups to Vdd. Every vendors' Phy is different in that regard.
In ALL cases, I recommend using a transformer for coupling. Not is it only safer for you and the equipment, the transformers don't cost much. If space is an issue, find a RJ45 jack with internal magnetics.
...kevin