USB4640 datasheet(23/64 Pages) SMSC

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

Datasheet

SMSC USB4640/USB4640i

Revision 1.0 (06-09-09)

DATASHEET

Port Power control using a Poly Fuse

When using the USB4640/USB4640i with a poly fuse, an external diode must be used (See

Figure 6.2). 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 Schmitt trigger input will register this as a low resulting in an over-current detection. The open drain

output does not interfere.

Figure 6.2 Port Power Control with a Single Poly Fuse and Multiple Loads

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

USB4640/40i

USB

Device

5 V

PRTCTL3

USB

Device

PRTCTL2

USB

Device

Poly Fuse

5 V

USB

Device

PRTCTL2

PRTCTL3

USB4640/40i

USB4640 Datasheet(PDF) 23 Page - SMSC Corporation