USB Hub with Integrated 10/100 Ethernet Controller

Datasheet

2.1.2Port Power Control Using a Poly Fuse

When using theLAN9512 with a poly fuse, an external diode must be used (See Figure 2.3). 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 3.3 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 0 volts. The anode of the diode will be at 0.7 volts, and the Schmidt trigger input will register this as a low, resulting in an overcurrent detection. The open drain output does not interfere.

5V

Poly Fuse

PRTCTL3

USB

Device

LAN9512

5V

Poly Fuse

PRTCTL2

USB

Device

Figure 2.3 Port Power Control with Poly Fuse

SMSC LAN9512

17

Revision 1.0 (04-20-09)

 

DATASHEET