USB7252P datasheet(40/64 Pages) MICROCHIP

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USB7252P

DS00003561A-page 40

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2018 - 2020 Microchip Technology Inc.

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. 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 cath-

ode 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.

8.3

Power Delivery

Power Delivery (PD) defines a mechanism for USB devices to negotiate for additional current and/or higher or lower

voltages from VBUS than are defined in the original USB 2.0, USB 3.0, or BC 1.2 specifications. The standard allows a

maximum supply of 100 W.

Devices obtain the power required to operate from VBUS and have the ability to negotiate power levels with external

power sources. A half-duplex protocol has been developed for power providers and consumers to negotiate power over

VBUS via a modulation scheme. This serial connection has a data rate of approximately 400 kbps.

USB Power Delivery Specification v3.0 defines a mechanism in which the hub shall support the capability to return the

PD specific capabilities of a device that is attached to any of its PD enabled downstream ports. Therefore, a mechanism

is provided in which the USB7252P is able to extract the capabilities of the device from the port power controller and

supply this information to the hub.

The USB7252P supports USB Power Delivery with up to 100W of power and Alternate Modes on the upstream port.

Native basic Type-C with integrated CC logic is supported on two of the downstream ports. The USB Power Delivery

firmware stack is executed within the hub and controls a Microchip UPD360/UPD350 (or equivalent) companion Type-

C controller. The two downstream Type-C ports include internal USB 3.2 Gen 1 multiplexers; no external multiplexer is

required for Type-C support.

All Power Delivery messages from the USB Host are handled in firmware. Each PD message is stored in a buffer for

the firmware to read. Responses are sent from a buffer populated by firmware. All PD class-specific requests are sup-

ported (GetBatteryStatus, SetPDFeature) as well as four USB device requests (WRITE_REG, READ_REG,

WRITE_MEM, READ_MEM).

Note:

Type-C ports may not utilize a Poly-Fuse port power implementation due to the requirements that VBUS

on Type-C ports must be discharged to 0V when no device is attached to the port.

FIGURE 8-3:

PORT POWER CONTROL USING A POLY FUSE

PRT_CTLx

50k

PRTPWR

OCS

USB

Device

Pull-Up Enable

Poly Fuse

FILTER

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