to activate the pull-up resistor ?
The PIN input like all of the control lines is a 3.3V digital input so anywhere
from 2.3-3.3V will do the job. The digital inputs are 3.3V logic independent of
the Vbus voltage. Do not apply more than 4V to that input, it will back bias
the protection diode. We use an internal regulator to run all of the internal
logic at 3.3V. If Vbus and Vdd are connected together, they should be run at
3.3V anyway so the answer still holds.