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USB Disconnect circuit

Question asked by ferner.joe on Aug 19, 2014
usb-disconnect.jpg

I've been looking through STM32 development board circuits to find the best way to connect the USB disconnect. I found the above circuit from the STM3210E-EVAL board, but all of the ST boards appear to have similar layouts. I have a couple questions about this layout:
       
  1. Why are there two transistors? Why isn't T2 sufficient?
  2.    
  3. Why are there transistors at all? Could USB_DP be connected to a GPIO via a resistor and toggle between floating and on?
  4.    
  5. If not 2, could a P-CH MOSFET with a low VGS be used instead?

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