Datasheet

High-Speed Inter-Chip (HSIC) USB 2.0 Hub and Flash Media Controller
Datasheet
Revision 1.3 (03-13-13) 20 SMSC USB4640/USB4640i
DATASHEET
3.5 Port Power Control
3.5.1 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 3.2 Port Power Control with USB Power Switch
3.5.2 Port Power Control Using a Poly Fuse
When using the USB4640/USB4640i with a poly fuse, an external diode must be used (see Figure 3.3).
When disabling port power, the USB4640/USB4640i will drive a 0. This procedure will have no effect
since the external diode will isolate the pin from the load. When port power is enabled, the
USB4640/USB4640i output driver is disabled, and the pull-up resistor is enabled which creates an
open drain output. This open drain output condition means that the pull-up resistor is providing 3.3
volts to the anode of the diode. If there is an over-current situation, the poly fuse will open. This will
cause the cathode of the diode to go to zero volts. The anode of the diode will be at 0.7 volts, and the
USB Power
Switch
5 V
USB
Device
PRTCTL3
EN
OCS
USB Power
Switch
5 V
USB
Device
PRTCTL2
EN
OCS
USB4640/40i