AT43USB325 datasheet(90/109 Pages) ATMEL

90 / 109 page

3355C–USB–4/05

AT43USB325

8.4.5

Hub and Port Power Management

Overcurrent protection and power switching are required for the external downstream ports only.

In the AT43USB325, these tasks are completely programmable. This means that any type of

hub is achievable with the AT43USB325: self-powered or bus-powered hubs, per port or global

overcurrent protection, individual or ganged port power switching.

The use of the MCU's GPIO pins are required to interface to the external power supply monitor-

ing and switching. The on-chip hardware of the AT43USB325 contains the circuitry to handle all

the possible combinations of port power management tasks. The firmware defines the exact

configuration.

8.4.6

Overcurrent Sensing

The AT43USB325 is capable of detecting overcurrent during active operation only, or during any

condition even when the hub is in the suspended state. When overcurrent in the active state only

is desired, any GPIO pin of the AT43USB325 can be used to sense and the overcurrent condi-

tion. Control of the condition must be performed by the firmware. If overcurrent detection under

any condition is desired, then specific GPIO pins must be used to sense the overcurrent and the

proper bit(s) of UOVCER set. In Global Overcurrent Protection mode, overcurrent sensing must

be routed to GPIO PD0. In Individual Port Overcurrent Protection mode Port2 and Port 3 over-

current sensing must be assigned to GPIO PD0 and PD1. In the following description, it is

assumed that overcurrent protection is required under any condition.

Global Overcurrent Protection – In this mode, the Port Overcurrent Indicator and Port

Overcurrent Indicator Change should be set to 0's. For the AT43USB325 an external

solid state switch, such as the Micrel MIC2025-2, is required to switch power to the

external USB ports. The FLG output of the switch should be connected to PD0. When

an overcurrent occurs, FLG is asserted and the firmware should set the Hub Overcur-

rent Indicator and Hub Overcurrent Indicator Change and switch off power to all

external downstream ports. The hub status change is reported on the next IN token

through the hub's interrupt endpoint, Endpoint1.

Individual Port Overcurrent Protection – The Hub Overcurrent Indicator and Hub

Overcurrent Indicator Change bits should be set to 0's. One MIC2026-2 is required for

the two USB ports. The FLG output of the MIC2026-2 associated with Port2 should be

connected to GPIO PD0 and the other FLG output to PD1. An overcurrent is indicated

by assertion of FLG. The firmware sets the corresponding port's Overcurrent Indicator

and the Overcurrent Indicator Change bits and switches off power to the port. At the

next IN token from the Host, the AT43USB325 reports the port status change through

the hub's Endpoint1.

8.4.7

Port Power Switching

Gang Power Switching – One of the microcontroller GPIO pins, PWRN, must be pro-

grammed as an output to control the external switch such as the MIC2025-2. Switch

ON is requested by the USB Host through the SetPortFeature(PORT_POWER)

request. Switch OFF is executed upon receipt of a ClearPortFeature(PORT_POWER)

or upon detecting an overcurrent condition. The firmware clears the Power Control Bit.

Only if all of the Power Control Bits of ports 2 and 3 are cleared should the firmware de-

assert the PWRN pin.

Individual Power Switching – Two microcontroller GPIO pins, PWR2N and PWR3N,

must be assigned for each USB port to control the external switch such as the

MIC2026-2. Each of the Power Control Bits controls one PWRxN.

Multiple Ganged Overcurrent Protection – Overcurrent sensing is grouped physi-

cally into one or more gangs, but reported individually.

AT43USB325 Datasheet(PDF) 90 Page - ATMEL Corporation

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