USB4640-HZH SMSC [SMSC Corporation], USB4640-HZH Datasheet - Page 22

• Manufacturer Part Number: USB4640-HZH
• Description: High Speed Inter-Chip (HSIC) USB 2.0 Hub and Flash Media Controller
• Manufacturer: SMSC [SMSC Corporation]

Revision 1.0 (06-09-09)
6.3
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.
Port Power Control
Figure 6.1 Port Power Control with USB Power Switch
USB4640/40i
DATASHEET
High Speed Inter-Chip (HSIC) USB 2.0 Hub and Flash Media Controller
22
PRTCTL3
PRTCTL2
EN
EN
OCS
OCS
USB Power
USB Power
Switch
Switch
Device
Device
USB
USB
5 V
5 V
SMSC USB4640/USB4640i
Datasheet