AT43USB326 datasheet(72/102 Pages) ATMEL

72 / 102 page

AT43USB326

3313D–USB–04/06

Figure 12 shows a simplified diagram of a power management circuit of an AT43USB326

based hub design with global overcurrent protection and ganged power switching for the two

external downstream ports.

The over-current protection and port power switching for the AT43USB326 is best imple-

mented in the so-called multiple gang. The Hub Characteristic’s bits in the Hub Descriptor are

set as follows:

•

Logical Power Switching is Individual, D1D0 = 01

•

Overcurrent Protection is Individual, D4D3 = 01

When an over-current condition at one of the external ports is detected, the over-current bits of

both external ports are set. The host will switch off power to the external port, but the keyboard

will continue to operate. The external port power is switched on as soon as one port's power is

enabled, but switched off only when the power to both ports is disabled.

Figure 12. Port Power Management

Suspend and

Resume

The AT43USB326 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.

CTL

FLG

OUT

SWITCH

AT43USB326

GND

VCC

PWRN

OVCN

PORT2_POWER

PORT2_GND

PORT3_POWER

PORT3_GND

BUS_POWER

GND

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