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Re: Static Discharge


Rick Brooks wrote:


a few comments:
RJ-45 pins will almost always not mate within the same few microsecond period, so there is always
some differential mode, some pair to pair mode, and some common mode currents generated by cable discharge.

Yes, the PHY must be protected, internally, or otherwise, since at ESD frequencies, the magnetics pass most of the
differential mode energy, and some common mode energy.

Do we really need the MOV to protect the PSE output when it will probably have a large output cap, and smaller caps for EMC?

I agree the large output cap is a good protector for the PSE.
I'm worried about the off state and the case where a power supply is not connected.

Maybe, but that is an implementation detail.

As far as protecting silicon on the wire, we need to know what type of silicon process we are talking about.
A 60V power process can obviously withstand a lot more abuse on the wire than a low voltage, high speed PHY process.
One of those the devil is in the details types of problems.

The MOSFET switch needs to be 60V rugged.
The control circuits can use attenuators to drop the voltage.
This is probably an implementation choice.

- Rick