AT90USB64/128
8.1
Internal Voltage Reference
AT90USB64/128 features an internal bandgap reference. This reference is used for Brown-out
Detection, and it can be used as an input to the Analog Comparator or the ADC.
8.1.1
Voltage Reference Enable Signals and Start-up Time
The voltage reference has a start-up time that may influence the way it should be used. The
start-up time is given in Table 8-4. To save power, the reference is not always turned on. The
reference is on during the following situations:
1. When the BOD is enabled (by programming the BODLEVEL [2..0] Fuse).
2. When the bandgap reference is connected to the Analog Comparator (by setting the
ACBG bit in ACSR).
3. When the ADC is enabled.
Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user
must always allow the reference to start up before the output from the Analog Comparator or
ADC is used. To reduce power consumption in Power-down mode, the user can avoid the three
conditions above to ensure that the reference is turned off before entering Power-down mode.
Table 8-4.
Symbol Parameter
VBG Bandgap reference voltage
tBG
Internal Voltage Reference Characteristics(1)
Condition Min
Typ
1.1
40
Max Units
TBD
TBD
TBD
TBD
70
V
Bandgap reference start-up time
µs
Bandgap reference current
consumption
IBG
TBD
10
TBD
µA
Note:
1. Values are guidelines only. Actual values are TBD.
8.2
Watchdog Timer
AT90USB64/128 has an Enhanced Watchdog Timer (WDT). The main features are:
• Clocked from separate On-chip Oscillator
• 3 Operating modes
– Interrupt
– System Reset
– Interrupt and System Reset
63
7593A–AVR–02/06
ATMEL [ ATMEL ]
