ATMEGA169P-15AT Datasheet, PDF (50/373 Pages) ATMEL Corporation – 8-bit Microcontroller with 16K Bytes In-System Programmable Flash

9.2.3
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 9-5), the Brown-out Reset is immediately activated.
When V_CC increases above the trigger level (V_BOT+ in Figure 9-5), 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 328.
Figure 9-5. Brown-out Reset During Operation
V_CC
V_BOT-
V_BOT+
RESET
TIME-OUT
t_TOUT
9.2.4
Watchdog Reset
INTERNAL
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
page 51 for details on operation of the Watchdog Timer.
Figure 9-6. Watchdog Reset During Operation
CC
CK
50 ATmega169P Automotive
7735B–AVR–12/07