Is there a risk of back feeding from a powered usb hub?

I have a number of higher powered usb devices, and I’m planning on using a powered hub. However I intend to have the board and usb run off of a battery power supply. I have the carrier board running at 15v input, and I would use a buck converter to provide 5v to the usb hub and some other modules.

So could I for example have a relay or mosfet connected to the 3.3v out on the board so that the usb hub is only powered when the board starts up?

It is quite common to use an externally powered USB HUB, especially for USB debugging. Any normal USB HUB with external power is a benefit. However, I don’t know if you mean a HUB of your own design…certainly any off-the-shelf HUB, plus your power supply, is ok. A typical powered HUB functions as a normal unpowered HUB whenever external power is not present, and so if you want this HUB to not draw power from either the HUB or the Jetson during boot, then you’d have to come up with some way to disconnect entirely (power wise) until you are at the desired boot stage. I won’t guarantee it, but I suspect if you simply cut any USB socket +5V wire between the Jetson and the HUB, and provide power just via the HUB’s external supply, I suspect it will work (no guarantee). Then your MOSFET should work if the voltage drop from the MOSFET still leaves the supply voltage within spec.

Basically, USB is “plug-n-play”. This means the Jetson should detect devices connecting or disconnecting and “do the right thing”. A device which is unpowered should simply not show up, and adding power should be equivalent to a device plugin. The only real question is if your power add/cut is clean and works at whatever voltage the HUB needs (I am thinking off-the-shelf powered HUB).

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