Ultra Fast USB 2.0 Multi-Format Flash Media Controller/USB Hub Combo

6.3Port 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.

USB2640/USB2641

5V

PRTCTL3

OCS

USB Power

Switch

EN

USB

Device

5V

PRTCTL2

OCS

USB Power

Switch

EN

USB

Device

Figure 6.1 Port Power Control with USB Power Switch

Revision 2.0 (10-03-08)

24

SMSC USB2640/USB2641

 

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