Datasheet

Figure 15-5. Brown-out Reset During Operation
V
CC
RESET
TIME-OUT
INTERNALRESET
V
BOT-
V
BOT+
t
TOUT
15.6 Watchdog System Reset
When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On the falling
edge of this pulse, the delay timer starts counting the Time-out period t
TOUT
.
Figure 15-6. Watchdog System Reset During Operation
CK
CC
15.7 Internal Voltage Reference
The device 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.
15.7.1 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. 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] Fuses).
2. When the bandgap reference is connected to the Analog Comparator (by setting the ACBG bit in
ACSR (ACSR.ACBG)).
3. When the ADC is enabled.
Thus, when the BOD is not enabled, after setting ACSR.ACBG 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 the Power-Down mode, the user can avoid the three conditions above to
ensure that the reference is turned OFF before entering Power-Down mode.
ATmega48PA/88PA/168PA
System Control and Reset
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40002011A-page 81