at90usb647-16au ATMEL Corporation, at90usb647-16au Datasheet - Page 26

• Manufacturer Part Number: at90usb647-16au
• Description: At90usb1286 8-bit Avr Microcontroller With 64/128k Bytes Of Isp Flash And Usb Controller
• Manufacturer: ATMEL Corporation

8.4
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AT90USB1287/6 Third Release
AT90USB64/128
4. Transient perturbation in USB suspend mode generates overconsumption
3. Spike on TWI pins when TWI is enabled
2. High current consumption in sleep mode
1. Asynchronous timer interrupt wake up from sleep generates multiple interrupts
• 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
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.
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.
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.
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.
7593GS–AVR–03/08