This is my third revision of this supply switching circuit. Do you guys see any problem with this revision?
This is a circuit to switch from disposable lithium battery to USB power when the device is plugged into a computer. Q1 and Q2 are PFETs. When there's no USB power, both FETs Vgs is -3.6v. When USB is plugged in, the USB interface IC sends 3.3v to the FETs gates, sufficiently turning Q1 and Q2 off. VBUS is a regulated voltage from USB. The diode to is keep from back feeding the regulator when there's no USB power.
I can't use an ORing diode circuit, I cant afford the parasitic losses. The losses from the diode on VBUS are fine since it won't be from the battery.