SMSC USB2640i - Manual (Page 24)

Ultra Fast USB 2.0 Multi-Format Flash Media Controller/USB Hub Combo
Revision 2.0 (10-03-08) 24 SMSC USB2640/USB2641
DATASHEET
6.3 Port Power Control
Port Power Control Using USB Power Switch
The USB2640/USB2641 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 recognize this situation as a low. The open drain output does not interfere.
The 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
USB2640/
USB2641
USB Power
Switch
5V
USB
Device
PRTCTL3
EN
OCS
USB Power
Switch
5V
USB
Device
PRTCTL2
EN
OCS