AT43301
6
Bus-Powered Mode
In the bus-powered mode all the power for the hub itself as
well as the downstream ports is supplied by the root hub or
upstream hub through the USB. Only 100 mA is available
for each of the hub’s downstream devices and therefore
only low-power devices are supported.
The power switch works exactly like the self-powered
mode, except that the allowable switch resistance is higher:
140 m
Ω
or less under the worst case condition. An exam-
ple of a suitable high side switch for a bus-powered hub is
the Micrel MIC2525.
The diagrams of Figure 2 and Figure 3 show examples of
the power supply and power management scheme in the
self-powered mode and bus-powered mode using an inte-
grated switch with built-in overcurrent protection.
Figure 2. Bus-powered Hub
Figure 3. Self-powered Hub
BUS_POWER
GND
GND
VCC
AT43301
PWR
OVC
U1
CTL
FLG
IN
OUT
SWITCH
U2
PORT_POWER
GND
PORT_POWER
GND
PORT_POWER
GND
PORT_POWER
GND
TO
DOWNSTREAM
DEVICES
BUS_POWER
GND
GND
VCC
AT43301
PWR
OVC
U1
CTL
FLG
IN
OUT
SWITCH
U2
PORT_POWER
GND
PORT_POWER
GND
PORT_POWER
GND
PORT_POWER
GND
TO
DOWNSTREAM
DEVICES
POWER SUPPLY
5V OUT
GND
PS5
