High Speed Inter-Chip USB 2.0 Hub and Flash Media Controller

Datasheet

6.3Port 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.

5 V

PRTCTL3

OCS

USB Power

Switch

EN

USB

USB4640/40iDevice

5 V

PRTCTL2

OCS

USB Power

Switch

EN

USB

Device

Figure 6.1 Port Power Control with USB Power Switch

Revision 1.0 (06-01-09)

22

SMSC USB4640/USB4640i

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