USB2640I Standard Microsystems Corp., USB2640I Datasheet - Page 25

• Manufacturer Part Number: USB2640I
• Description: Industrial Temperature Usb 2.0 Flash Media Controller And Usb Hub Combo
• Manufacturer: Standard Microsystems Corp.

Industrial Temperature USB 2.0 Flash Media Controller and USB Hub Combo
SMSC USB2640i/USB2641i
Port Power Control Using a Poly Fuse
When using the USB2640i/USB2641i with a poly fuse, an external diode must be used (See Figure
6.2). When disabling port power, the driver 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 output driver is
disabled, and the pull-up resistor is enabled which creates an open drain output. This means that the
pull-up resistor is providing 3.3V 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 0V. The anode of the diode will
be at 0.7V, and the Schmitt trigger input will register this as a low resulting in an over-current detection.
The open drain output does not interfere.
When using a single poly fuse to power all devices, note that for the ganged situation, all power control
pins must be tied together.
Figure 6.3 Port Power with Ganged Control with Poly Fuse
USB2640i/
USB2641i
Figure 6.2 Port Power control with Poly Fuse
USB2640i/
USB2641i
DATASHEET
25
PRTCTL2
PRTCTL3
PRTCTL3
PRTCTL2
Device
Device
USB
USB
5V
5V
Device
USB
5V
Revision 2.0 (10-03-08)
Poly Fuse
Device
USB