External power-management devices, such as the TPS2044, are required to control the 5-V source to the downstream ports according to the corresponding values of the PWRON pin. Upon detecting any overcurrent conditions, the power-management device sets the corresponding OVRCUR pin of the TUSB2046x to a logic low. If GANGED is high, all PWRON outputs switch together and if any OVRCUR is activated, all ports transition to the power-off state. If GANGED is low, the PWRON outputs and OVRCUR inputs operate on a per-port basis.
Both bus-powered and self-powered hubs require overcurrent protection for all downstream ports. The two types of protection are individual-port management (individual-port basis) or ganged-port management (multiple-port basis). Individual-port management requires power-management devices for each individual downstream port, but adds robustness to the USB system because, in the event of an overcurrent condition, the USB host only powers down the port that has the condition. The ganged configuration uses fewer power-management devices and thus has lower system costs, but in the event of an overcurrent condition on any of the downstream ports, all the ganged ports are disabled by the USB host.
Using a combination of the BUSPWR and EEDATA/GANGED inputs, the TUSB2046x supports four modes of power management: bus-powered hub with either individual-port power-management or ganged-port power management, and the self-powered hub with either individual-port power management or ganged-port power management. TI supplies the complete hub solution with the TUSB2036 (2/3-port), TUSB2046x, and the TUSB2077 (7-port) hubs along with the power-management devices needed to implement a fully USB specification-compliant system.