Datasheet

49
ATmega169A/PA/329A/PA/649A/P/3290A/PA/6490A/P [DATASHEET]
8284E–AVR–02/2013
11.2.3 Brown-out detection
The Atmel ATmega169A/169PA/329A/329PA/3290A/3290PA/649A/649P/6490A/6490P has an On-chip Brown-out
Detection (BOD) circuit for monitoring the V
CC
level during operation by comparing it to a fixed trigger level. The
trigger level for the BOD can be selected by the BODLEVEL Fuses. The trigger level has a hysteresis to ensure
spike free Brown-out Detection. The hysteresis on the detection level should be interpreted as V
BOT+
= V
BOT
+
V
HYST
/2 and V
BOT-
= V
BOT
- V
HYST
/2.When the BOD is enabled, and V
CC
decreases to a value below the trigger level
(V
BOT-
in Figure 11-5), the Brown-out Reset is immediately activated. When V
CC
increases above the trigger level
(V
BOT+
in Figure 11-5), the delay counter starts the MCU after the Time-out period t
TOUT
has expired.
The BOD circuit will only detect a drop in V
CC
if the voltage stays below the trigger level for longer than t
BOD
given
in ”System and reset characteristics” on page 334.
Figure 11-5. Brown-out reset during operation.
11.2.4 Watchdog 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
. Refer to ”Watchdog Timer” on page 50 for
details on operation of the Watchdog Timer.
Figure 11-6. Watchdog reset during operation.
V
CC
RESET
TIME-OUT
INTERNAL
RESET
V
BOT-
V
BOT+
t
TOUT
CK
CC