Datasheet

421
7766F–AVR–11/10
ATmega16/32U4
35.5 ATmega16U4/ATmega32U4 Rev A
• Spike on TWI pins when TWI is enabled
• High current consumption in sleep mode
• Increased power consumption in power-down mode
• Internal RC oscillator start up may fail
• Internal RC oscillator calibration
• Incorrect execution of VBUSTI interrupt
• Timer 4 enhanced mode issue
1. Spike on TWI pins when TWI is enabled
100 ns negative spike occurs on SDA and SCL pins when TWI is enabled.
Problem Fix/work around
Enable ATmega16U4/ATmega32U4 TWI before the other 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/work around
Before entering sleep, interrupts not used to wake up the part from the sleep mode should
be disabled.
3. Increased power comsumption in power-down mode
The typical power consumption is increased by about 30 µA in power-down mode.
Problem Fix/work around
None.
4. Internal RC oscillator start up may fail
When the part is configured to start on internal RC oscillator, the oscillator may not start
properly after power-on.
Problem Fix/work around
Do not configure the part to start on internal RC oscillator.
5. Internal RC oscillator calibration
8 MHz frequency can be impossible to reach with internal RC even when using maximal
OSCAL value.
Problem Fix/work around
None.
6. Incorrect execution of VBUSTI interrupt
The CPU may incorrectly execute the interrupt vector related to the VBUSTI interrupt flag.
Problem fix/work around
Do not enable this interrupt. Firmware must process this USB event by polling VBUSTI.