USB82640 datasheet(17/64 Pages) MICROCHIP

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DS60001312A-page 17

USB82640

5.3.2

PORT POWER CONTROL USING A POLY FUSE

When using the USB82640 with a poly fuse, an external diode must be used (see Figure 5-2). When disabling port

power, the USB82640 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 USB82640 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 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.

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 5-2:

PORT POWER CONTROL WITH SINGLE POLY FUSE AND MULTIPLE LOADS

FIGURE 5-3:

PORT POWER CONTROL WITH GANGED CONTROL WITH POLY FUSE

USB

Device

5 V

PRTCTL3

USB

Device

5 V

PRTCTL2

USB82640

USB

Device

Poly Fuse

5 V

USB

Device

PRTCTL2

PRTCTL3

USB82640

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