466130 Datasheet, PDF (27/36 Pages) ATMEL Corporation – 8-bit Microcontroller with 64/128K Bytes of ISP Flash

7593JS–AVR–03/09
ATmega32U6/AT90USB64/128
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.
6. 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.
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 ATmega32U6/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
27