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DS00002774G-page 23

USB4712

8.6

USB to UART Bridging

The USB to UART bridging feature of the USB4712 provides system designers with expanded system control and

potential BOM reduction. When using Microchip’s USB hubs, a separate USB to UART device is no longer required and

a downstream USB port is not lost, as occurs when a standalone USB to UART device is implemented.

Commands may be sent from the USB Host to the internal Hub Feature Controller device in the Microchip hub to per-

form the following functions:

• Enable/Disable UART Interface

• Set UART Interface Baud Rate

•UART Write

•UART Read

For detailed information on utilizing the USB4712 USB to UART bridging feature, refer to the application note “USB to

UART Bridging with Microchip USB4712 Hub

”.

8.7

Link Power Management (LPM)

The device supports the L0 (On), L1 (Sleep), and L2 (Suspend) link power management states. These supported LPM

states offer low transitional latencies in the tens of microseconds versus the much longer latencies of the traditional USB

suspend/resume in the tens of milliseconds. The supported LPM states are detailed in Table 8-1.

8.8

Port Power Control

Port power and over-current sense share the same pin (PRT_CTL1/OCS1) for each port. These functions can be con-

trolled directly from the USB hub, or via the processor.

8.8.1

PORT CONNECTION IN COMBINED MODE

8.8.1.1

Port Power Control using USB Power Switch

When operating in combined mode, the device will have one port power control and over-current sense pin for each

downstream port. When disabling port power, the driver will actively drive a '0'. To avoid unnecessary power dissipation,

the pull-up resistor will be disabled at that time. When port power is enabled, it will disable the output driver and enable

the pull-up resistor, making it an open drain output. If there is an over-current situation, the USB Power Switch will assert

the open drain OCS signal. The Schmidt trigger input will recognize that as a low. The open drain output does not inter-

fere. The over-current sense filter handles the transient conditions such as low voltage while the device is powering up.

TABLE 8-1:

LPM STATE DEFINITIONS

State

Description

Entry/Exit Time to L0

L2

Suspend

Entry: ~3 ms

Exit: ~2 ms (from start of RESUME)

L1

Sleep

Entry: <10 us

Exit: <50 us

L0

Fully Enabled (On)

-