USB Hub with Integrated 10/100 Ethernet Controller

Datasheet

2.1.2Port Power Control Using a Poly Fuse

When using theLAN9514 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

5V

Poly Fuse

Poly Fuse

PRTCTL4

PRTCTL3

USB

 

USB

Device

 

Device

 

 

 

 

LAN9514

5V

5V

Poly Fuse

Poly Fuse

PRTCTL5

PRTCTL2

 

USB

 

 

 

 

USB

 

Device

 

 

 

Device

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2.3 Port Power Control with Poly Fuse

SMSC LAN9514

17

Revision 1.0 (04-20-09)

 

DATASHEET