26

7593GS–AVR–03/08

AT90USB64/128

8.4

AT90USB1287/6 Third Release

• Transient perturbation in USB suspend mode generates over consumption

• Spike on TWI pins when TWI is enabled

• High current consumption in sleep mode

• Async timer interrupt wake up from sleep generate multiple interrupts4

4

.

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. The internal USB engine remains in suspend mode but the USB differ-

ential receiver is still enabled and generates a typical 300µA extra-power consumption.

Detection of the suspend state after the transient perturbation should be performed by soft-

ware (instead of reading the SUSPI bit).

Problem fix/workaround

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

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, before 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 sleep mode should be

disabled.

1.

Asynchronous timer interrupt wake up from sleep generates multiple interrupts

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

then goes back into sleep mode, it may wake up multiple times.