I'm building a USB device that can be power by a external 5V supply or from the USB bus. The device can be used without USB, so i need the option of the external 5v source. I have a 5V regulating circuit for the external source. The 5V external source and usb bus power are both connected in parallel.
Should I use a diode on the USB +Vbus in case both sources are connected and the USB connection is in sleep mode?