The downstream port power, VBUS, must be supplied
by a source capable of supplying 5V and at least 500mA per port. Downstream port
power switches can be controlled by the TUSB4020BI-Q1
signals. It is possible to leave the downstream port power always enabled.
Each downstream port’s VBUS requires a large bulk low-ESR capacitor of 22µF or larger to limit in-rush current.
TI recommends ferrite beads on the VBUS pins of the downstream USB port connections for both ESD and EMI reasons. A 0.1µF capacitor on the USB connector side of the ferrite provides a low-impedance path to ground for fast rise time ESD current that might have coupled onto the VBUS trace from the cable.