Brown-out Detection

The device has an on-chip Brown-out Detection (BOD) circuit for monitoring the VCC 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 VBOT+ = VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2. When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in the following figure), the Brown-out Reset is immediately activated. When VCC increases above the trigger level (VBOT+ in the following figure), the delay counter starts the MCU after the Time-out period tTOUT has expired.

The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level for longer than tBOD.

Figure 1. Brown-out Reset During Operation