Datasheet

50
8018P–AVR–08/10
ATmega169P
10.2.3 Brown-out Detection
ATmega169P 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 10-5), the Brown-out Reset is immediately acti-
vated. When V
CC
increases above the trigger level (V
BOT+
in Figure 10-5), 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 lon-
ger than t
BOD
given in ”System and Reset Characteristics” on page 333.
Figure 10-5. Brown-out Reset During Operation
10.2.4 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 51 for details on operation of the Watchdog Timer.
Figure 10-6. Watchdog Reset During Operation
V
CC
RESET
TIME-OUT
INTERNAL
RESET
V
BOT-
V
BOT+
t
TOUT
CK
CC