SMSC LAN9512 - Manual (Page 16)

USB Hub with Integrated 10/100 Ethernet Controller
Datasheet
Revision 1.0 (04-20-09) 16 SMSC LAN9512
DATASHEET
2.1 Port Power Control
This section details the usage of the port power control pins PRTCTL[3:2].
2.1.1 Port Power Control Using a USB Power Switch
The LAN9512 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 overcurrent sense filter
handles the transient conditions, such as low voltage, while the device is powering up.
Figure 2.2 Port Power Control with USB Power Switch
USB Power
Switch
EN
OCS
5V
USB
Device
LAN9512
PRTCTL3
USB Power
Switch
EN
OCS
5V
USB
Device
PRTCTL2