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I was looking at the teensy 4.0 schematic, and I noticed that there was a transistor with its gate connected to ground attached to the USB power supply line that goes to the processor. If the gate is tied to ground, wouldn't this just act as a diode? Is there any reason this was chosen over a diode, or is it performing some function I am unaware of?

Links to relevant parts:

Teensy 4.0 Schematic
Transistor datasheet