at90usb647-16au ATMEL Corporation, at90usb647-16au Datasheet - Page 24

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

8.3
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AT90USB1287/6 Second Release
AT90USB64/128
6.
5.
4.
3. Spike on TWI pins when TWI is enabled
2. High current consumption in sleep mode
• 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
The low to high transition of D- violates the USB eye diagram specification when transmitting
with low-speed signaling.
Problem fix/workaround
None.
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.
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.
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.
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.
USB Eye Diagram violation in low-speed mode
Transient perturbation in USB suspend mode generates overconsumption
VBUS Session valid threshold voltage
7593GS–AVR–03/08