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7593GS–AVR–03/08

AT90USB64/128

The VSession valid threshold voltage is internally connected to VBus_Valid (4.4V approx.).

That causes the device to attach to the bus only when Vbus is greater than VBusValid

instead of V_Session Valid. Thus if VBUS is lower than 4.4V, the device is detached.

Problem fix/workaround

According to the USB power drop budget, this may require connecting the device toa root

hub or a self-powered hub.

5.

UBS signal rate

The average USB signal rate may sometime be measured out of the USB specifications

(12MHz ±30kHz) with short frames. When measured on a long period, the average signal

rate value complies with the specifications. This bit rate deviation does not generates com-

munication or functional errors.

Problem fix/workaround

None.

4.

VBUS residual level

In USB device and host mode, once a 5V level has been detected to the VBUS pad, a resid-

ual level (about 3V) can be measured on the VBUS pin.

Problem fix/workaround

None.

3.

Spike on TWI pins when TWI is enabled

100 ns negative spike occurs on SDA and SCL pins when TWI is enabled.

Problem Fix/workaround

No known workaround, enable AT90USB64/128 TWI first versus the others nodes of the

TWI network.

2.

High current consumption in sleep mode

If a pending interrupt cannot wake the part up from the selected mode, the current consump-

tion will increase during sleep when executing the SLEEP instruction directly after a SEI

instruction.

Problem Fix/workaround

Before entering sleep, interrupts not used to wake up the part from the sleep mode should

be disabled.

1.

Asynchronous timer interrupt wake up from sleep generates multiple interrupts

If the CPU core is in sleep and wakes-up from an asynchronous timer interrupt and then go

back in sleep again it may wake up multiple times.

Problem Fix/workaround

A s o ft wa r e wo r k ar o un d i s to w ai t wi t h pe r fo r mi n g th e s l ee p i n st r uc t io n u nt i l

TCNT2>OCR2+1.