USB4715

DS00002514B-page 28

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2022 Microchip Technology Inc. and its subsidiaries

8.8.2.2

Port Power Control using Poly Fuse

When using the device with a poly fuse, there is no need for an output power control. To maintain consistency, the same

circuit will be used. A single port power control and over-current sense for each downstream port is still used from the

Hub's perspective. When disabling port power, the driver will actively drive a '0'. This will have no effect as the external

diode will isolate pin from the load. When port power is enabled, it will disable the output driver and enable the pull-up

resistor. 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 over-current detection. The open

drain output does not interfere.

FIGURE 8-2:

PORT POWER CONTROL WITH USB POWER SWITCH

FIGURE 8-3:

PORT POWER CONTROL USING A POLY FUSE

USB Power

Switch

50k

PRTPWR

EN

OCS

OCS

Pull‐Up Enable

5V

USB 

Device

FILTER

PRT_CTLx

PRT_CTLx

50k

PRTPWR

OCS

USB

Device

Pull-Up Enable

5V

Poly Fuse

FILTER