lan9512 Standard Microsystems Corp., lan9512 Datasheet - Page 17

• Manufacturer Part Number: lan9512
• Description: Usb Hub With Integrated 10/100 Ethernet Controller
• Manufacturer: Standard Microsystems Corp.

USB Hub with Integrated 10/100 Ethernet Controller
Datasheet
SMSC LAN9512
2.1.2
Port Power Control Using a Poly Fuse
When using theLAN9512 with a poly fuse, an external diode must be used (See
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.
LAN9512
Figure 2.3 Port Power Control with Poly Fuse
DATASHEET
PRTCTL3
PRTCTL2
17
Device
Device
USB
USB
5V
5V
Poly Fuse
Poly Fuse
Revision 1.0 (04-20-09)
Figure
2.3). When