# How does this PMOS circuit work?

I've been trying to figure out how this PMOS circuit is functioning.

B_VCC is 5V coming from a USB port on the board, while VCC5V is used elsewhere in a regulator to create 3.3V but otherwise does not exist anywhere else. PSELF is effectively grounded as nothing is being plugged into the DC Jack.

When USB is plugged in and nothing is plugged into the DC jack, B_VCC goes to 5V which is understandable but VCC5V goes to 5V as well, which means the transistor must be on. For it to turn on, the conditions are that the PMOS is either in Linear or Saturation.

$V_{sd}$=floating-5V ; $V_{sg}$ = floating-0V ; $V_t$ = -0.8V (from datasheet)

$V_{sd} < V_{sg} – \vert V_t\vert$ LINEAR

TRUE

$V_{sd} > V_{sg} – \vert V_t\vert$ SATURATION

FALSE

Is it okay to assume that the floating VCC5V is 0V?

Also after VCC5V goes to 5V, then $V_{sd}=0$, $V_{sg}$=-5V and $V_t$ = -0.8V so it would then move to Saturation mode?