Hot-plugging a passive PoE connection will blow your teensy PHY. Even though the PHY is DC-isolated from the jack, the unbalanced condition that occurs while hot plugging a powered cable will cause a transient spike of the order of your PoE voltage on your PHY. If you actually make this mistake, only the PHY is damaged and you can fix your teensy by replacing it (PN:dp83825irmqr). Robin very generously sent me some spares they had around and I was able to bring my dead teensies back to life. Thanks Robin!!!

The solution to this is easy: TSV diodes on the ethernet data lines on the PHY side + small series resistors. Implementing this on the next teensy revision or the ethernet adapter board or on your custom PCB will protect your PHY from hotplugging passive PoE.

This application note explains all this in detail. http://ww1.microchip.com/downloads/e.../00002157B.pdf