TUSB2046bi应用问题

TUSB2046bi，应用上有两个模式BUS Powered hub 和self powered hub，两个模式通过BUSPWR引脚进行选择，并且不能动态选择模式。请问这两个模式有什么区别吗？

如果接线上我使用BUS Powered hub，但同时外部也有移动电源供电，会不会有问题？

例如我们有1个upstream Port，4个downstream Port，所有VBUS连接在一起，没有做过流保护，由前端upstream Port Vbus给后端4个downstream Port供电；由于前端跟upstream Port的主机只有一个USB接口（兼任电源充电），这边设计希望后端4个downstream Port的任意一个都可以给前端主机充电。即在BUS Powered hub设计的情况下，也可能会引入外部电源，请问这个设计是否会存在问题？感谢！

Sunny，您好

关于BUS Powered hub 和self powered hub这个供电模式的说明，请参考下面的说明。所以这两个模式只能选其一。

A bus-powered hub is a hub that draws all its power from the host computer's USB interface. It does not need a separate power connection. However, many devices require more power than this method can provide and will not work in this type of hub.

A USB's electric current is allocated in units of 100 mA up to a maximum total of 500 mA per port. Therefore a compliant bus powered hub can have no more than four downstream ports and cannot offer more than four 100 mA units of current in total to downstream devices (since the hub needs one unit for itself). If a device requires more units of current than the port it is plugged into can supply, the operating system usually reports this to the user.

In contrast, a self-powered hub is one that takes its power from an external power supply unit and can therefore provide full power (up to 500 mA) to every port. Many hubs can operate as either bus powered or self powered hubs.

外部电源通过USB接口给主机供电，这样的HUB需要支持Dynamic powered hubs，TUSB2046BI不支持。

更多介绍请查阅维基百科中的说明，http://en.wikipedia.org/wiki/USB_hub

谢谢

总线供电和自供电主要对下行端口的电流有影响，如果采用总线供电方式时，下行端口每个USB口提供100mA电流，所以只能支持低功率的USB设备，并且最多只能夸展4个下行端口，而采用自供电的方式每个USB端口则能提供500mA的电流，对下行端口的数量没有限制。