USB2642 datasheet(13/56 Pages) MICROCHIP

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DS00001578C-page 13

USB2642

5.3.2

PORT POWER CONTROL USING A POLY FUSE

When using the USB2642 with a poly fuse, an external diode must be used (see Figure 5-2). When disabling port power,

the USB2642 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 USB2642 output driver is disabled, and the pull-up resistor is enabled which cre-

ates 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.

FIGURE 5-1:

PORT POWER CONTROL WITH USB POWER SWITCH

USB2642

USB Power

Switch

5 V

USB

Device

PRTCTL3

OCS

USB Power

Switch

5 V

USB

Device

PRTCTL2

OCS

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