AT43USB355 datasheet(99/115 Pages) ATMEL

99 / 115 page

AT43USB355

2603G–USB–04/06

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.

Figure 27 shows a simplified diagram of a power management circuit of an AT43USB355

based hub design with global overcurrent protection and ganged power switching.

Figure 27. Port Power Management

Suspend and

Resume

The AT43USB355 enters suspend only when requested by the USB host through bus inactiv-

ity for at least 3 ms. The USB hardware would detect this request, sets the GLB_SUSP bit of

SPRSR, Suspend/Resume Register, and interrupts the microcontroller if the interrupt is

enabled. The microcontroller should shut down any peripheral activity and enter the Power

Down mode by setting the SE and SM bits of MCUCR and then executes the SLEEP instruc-

tion. The USB hardware shuts off the oscillator and PLL.

Global Resume

Global resume is signaled by a J to K state change on Port0. The USB hardware enables the

oscillator/PLL, propagates the RESUME signaling, and sets the RSM bit of the SPRSR, which

generates an interrupt. The microcontroller starts executing where it left off and services the

interrupt. As part of the ISR, the firmware clears the GLB_SUSP bit.

Remote Wakeup

While the AT43USB355 is in global suspend, resume signaling is also possible through

remote wakeup if the remote wakeup feature is enabled. Remote wakeup is defined as a port

CTL

FLG

OUT

SWITCH

AT43USB355

GND

VCC

PWRN

OVCN

PORT2_POWER

PORT2_GND

PORT3_POWER

PORT3_GND

BUS_POWER

GND

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