Maximum Allowable Current that can be Drawn from the Host by a USB Hub

Question: What is the maximum current a USB hub can draw from the host?

 

Answer:

 Bus-powered hubs may only draw up to one unit load upon power-up and upto five unit loads after configuration.

For self-powered hubs, power for the internal functions and downstream facing ports does not come from VBUS. However, the USB interface of the hub may draw up to one unit load from VBUS on its upstream facing port to allow the interface to function when the remainder of the hub is powered down.

Note:A unit load is defined to be 100 mA.