14.5 Brown-out Detection

The device 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 BOD. 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 the following figure), the Brown-out Reset is immediately activated. When V_CC increases above the trigger level (V_BOT+ in the following figure), 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.