>> >> >> Can I disable VBUS while keeping the rest of USB functional for a >> >> >> device that does not require bus power? >> >> > >> >> > unfortunately not, your device would see a disconnection. The reason is >> >> > that even though you don't really put any load on the bus, the PHY still >> >> > samples VBUS levels to know when the session is valid (VBUS > 4.4V). >> >> >> >> What if I use a USB cable with a separate DC input for the VBUS? >> > >> > What would be the point? I mean, if you've got a separate DC input for >> > Vbus then you aren't really saving any power or disabling anything. >> >> The point would be to minimize the amount of electrical noise the USB >> device is exposed to by using a low-noise supply for this such as a >> battery with a linear regulator. > > Okay. Is Vbus noise really a problem for you? I'm trying to see how far I can minimize the noise. >> > If you did this and then turned off the separate DC power, your device >> > wouldn't work afterward. As Felipe pointed out, the device would think >> > the cable had been disconnected. >> >> Understood. Can you tell me how to disable VBUS on the USB >> hub/controller? I'll be attempting this on a Beaglebone. > > I don't know what controller the Beaglebone uses. In general, however, > it isn't possible to disable Vbus on a USB host port and still use the > port. To do what you want, you would have to physically cut the Vbus > wire in the USB cable and splice the device side of that wire to the > external power supply. USB cables like that do exist for sale. Is there a way to disable VBUS on the host port if I use a cable like that? - Grant -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
