PIC® Device USB Host - Where do you connect the Vbus pin?
PIC32MZ: The Vbus pin must be connected to the 5 V USB output. The PIC32MZ USB module hardware is always running in OTG mode (even though the stack does not support OTG). It monitors the VBUS level to start and maintain the host session.
PIC32MX / PIC24 / dsPIC33: The Vbus pin can be left unconnected. The USB module hardware has three distinct operation modes, Host, Device and OTG. In Host mode, it does not monitor VBUS.