ATmega16HVB datasheet(45/273 Pages) ATMEL

45 / 273 page

8042A–AVR–07/09

ATmega16HVB/32HVB

Figure 11-4. Watchdog Reset During Operation

11.2.4

Brown-out Detection

ATmega16HVB/32HVB has an On-chip Brown-out Detection (BOD) circuit for monitoring the

CC level during operation by comparing it to a fixed trigger level VBOT. 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+ = VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.

The BOD is automatically enabled in all modes of operation, except in Power-off mode.

When the BOD is enabled, and V

CC decreases to a value below the trigger level (VBOT- 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 tTOUT has

expired.

Figure 11-5. Brown-out Reset During Operation

11.3

Reset and the Voltage Reference

The Voltage Reference is important for the performance of the system as the VREF voltage will

be used as reference voltage for several modules. It is therefore important to notice that after a

reset condition the Voltage Reference needs calibration and settling before the VREF voltage is

accurate. For details on Voltage Reference calibration and settling time, See ”Voltage Reference

and Temperature Sensor” on page 123.

FET

VCC

RESET

TIME-OUT

INTERNAL

RESET

VBOT-

VBOT+

tTOUT

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