USB5744

DS00001855K-page 28

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8.4.2.2

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 8-4:

DOUBLE LOW PULSE OVERCURRENT DETECTION

TABLE 8-2:

OVERCURRENT PULSE TIMING

Symbol

Description

Min

Max

Units

single low pulse assertion time

5

-

ms

double low pulse window

-

20

ms

Note:

The USB 2.0 and USB 3.2 Gen 1 bPwrOn2PwrGood descriptors must be set to 0 when using poly-fuse

mode. Refer to Microchip application note AN1903 “Configuration Options for the USB5734 and USB5744”

for details on how to change these values.

FIGURE 8-5:

PORT POWER CONTROL USING A POLY FUSE

PRT_CTLx

PRT_CTLx

50k

PRTPWR

OCS

USB

Device

Pull-Up Enable

5V

Poly Fuse

FILTER