24

7593GS–AVR–03/08

AT90USB64/128

8.3

AT90USB1287/6 Second Release

• USB Eye Diagram violation in low-speed mode

• Transient perturbation in USB suspend mode generates over consumption

• VBUS Session valid threshold voltage

• Spike on TWI pins when TWI is enabled

• High current consumption in sleep mode

• Async timer interrupt wake up from sleep generate multiple interrupts

6.

USB Eye Diagram violation in low-speed mode

The low to high transition of D- violates the USB eye diagram specification when transmitting

with low-speed signaling.

Problem fix/workaround

None.

5.

Transient perturbation in USB suspend mode generates overconsumption

In device mode and when the USB is suspended, transient perturbation received on the

USB lines generates a wake up state. However the idle state following the perturbation does

not set the SUSPI bit anymore. The internal USB engine remains in suspend mode but the

USB differential receiver is still enabled and generates a typical 300µA extra-power con-

sumption. Detection of the suspend state after the transient perturbation should be

performed by software (instead of reading the SUSPI bit).

Problem fix/workaround

USB waiver allows bus powered devices to consume up to 2.5mA in suspend state.

4.

VBUS Session valid threshold voltage

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.

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.