ATMEGA88 datasheet(43/349 Pages) ATMEL

43 / 349 page

ATmega48/88/168

2545D–AVR–07/04

Figure 19. External Reset During Operation

Brown-out Detection

ATmega48/88/168 has an On-chip Brown-out Detection (BOD) circuit for monitoring the

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

Notes:

1. VBOT may be below nominal minimum operating voltage for some devices. For

devices where this is the case, the device is tested down to VCC = VBOT during the

production test. This guarantees that a Brown-Out Reset will occur before V

CC drops

to a voltage where correct operation of the microcontroller is no longer guaranteed.

The

test

performed

using

BODLEVEL = 110

and

BODLEVEL = 101

for

ATmega48V/88V/168V,

and

BODLEVEL = 101

and

BODLEVEL = 101

for

ATmega48/88/168.

2. Min/Max values applicable for ATmega48.

When the BOD is enabled, and V

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

in Figure 20), the Brown-out Reset is immediately activated. When V

CC increases above

the trigger level (V

BOT+ in Figure 20), the delay counter starts the MCU after the Time-

out period t

TOUT has expired.

Table 21. BODLEVEL Fuse Coding(1)

BODLEVEL 2..0 Fuses

Min V

BOT

Typ V

BOT

Max V

BOT

Units

111

BOD Disabled

110

1.7

(2)

1.8

2.0

(2)

101

2.5

(2)

2.7

2.9

(2)

100

4.1

(2)

4.3

4.5

(2)

011

Reserved

010

001

000

Table 22. Brown-out Characteristics

Symbol

Parameter

Min

Typ

Max

Units

VHYST

Brown-out Detector Hysteresis

BOD

Min Pulse Width on Brown-out Reset

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