ATmega16U4 datasheet(51/408 Pages) ATMEL

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7766D–AVR–01/09

ATmega16U4/ATmega32U4

8.0.5

Brown-out Detection

ATmega16U4/ATmega32U4 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

BOT+ = VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.

When the BOD is enabled, and V

CC decreases to a value below the trigger level (VBOT- in Figure

8-5), the Brown-out Reset is immediately activated. When V

CC increases above the trigger level

BOT+ in Figure 8-5), the delay counter starts the MCU after the Time-out period tTOUT 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 Table 8-1.

Figure 8-5.

Brown-out Reset During Operation

Table 8-2.

BODLEVEL Fuse Coding

BODLEVEL 2..0 Fuses

Min VBOT

Typ VBOT

Max VBOT

Units

111

BOD Disabled

110

1.8

2.0

2.2

101

2.0

2.2

2.4

100

2.2

2.4

2.6

011

2.4

2.6

2.8

010

3.2

3.4

3.6

001

3.3

3.5

3.7

000

4.0

4.3

4.5

Table 8-3.

Brown-out Characteristics

Symbol

Parameter

Min

Typ

Max

Units

HYST

Brown-out Detector Hysteresis

tBOD

Min Pulse Width on Brown-out Reset

VCC

RESET

TIME-OUT

INTERNAL

RESET

VBOT-

VBOT+

tTOUT

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