The USB 3.1 specification allows the VBUS voltage to be as high as 5.5 V for normal operation, and as high as 20 V when the Power Delivery addendum is supported. Some applications require a max voltage to be 30 V.
The device requires the VBUS signal voltage be scaled down using an external resistor divider (as shown in the Figure 9-5), which limits the voltage applied to the actual device pin (USB0_VBUS, USB1_VBUS). The tolerance of these external resistors should be equal to or less than 1%, and the leakage current of zener diode at 5 V should be less than 100 nA.
The USB0_VBUS and USB1_VBUS pins can be considered to be fail-safe because the external circuit in Figure 9-5 limits the input current to the actual device pin in a case where VBUS is applied while the device is powered off.