SMSC USB464 - Manual (Page 22)

High Speed Inter-Chip USB 2.0 Hub and Flash Media Controller
Datasheet
Revision 1.0 (06-01-09) 22 SMSC USB4640/USB4640i
DATASHEET
6.3 Port Power Control
Port Power control using a USB Power Switch
The USB4640/USB4640i has a single port power control and over-current sense signal for each
downstream port. When disabling port power, the driver will actively drive a '0'. To avoid unnecessary
power dissipation, the internal pull-up resistor will be disabled at that time. When port power is enabled,
the output driver is disabled, and the pull-up resistor is enabled creating an open drain output.
If there is an over-current situation, the USB Power Switch will assert the open drain OCS signal. The
Schmitt trigger input will detect this event as a low. The open drain output does not interfere. The
internal over-current sense filter handles the transient conditions, such as low voltage, while the device
is powering up.
Figure 6.1 Port Power Control with USB Power Switch
USB Power
Switch
5 V
USB
Device
PRTCTL3
EN
OCS
USB Power
Switch
5 V
USB
Device
PRTCTL2
EN
OCS
USB4640/40i