ATMEGA3290 datasheet(43/375 Pages) ATMEL

43 / 375 page

ATmega329/3290/649/6490

2552H–AVR–11/06

teresis 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.

Note:

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 is performed using BODLEVEL = 10 for ATmega329/3290/649/6490V and

BODLEVEL = 01 for ATmega329/3290/649/6490L.

When the BOD is enabled, and V

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

in Figure 19), the Brown-out Reset is immediately activated. When V

CC increases above

the trigger level (V

BOT+ in Figure 19), 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 given in Table 16.

Figure 19. Brown-out Reset During Operation

Watchdog Reset

When the Watchdog times out, it will generate a short reset pulse of one CK cycle dura-

tion. On the falling edge of this pulse, the delay timer starts counting the Time-out period

TOUT. Refer to page 45 for details on operation of the Watchdog Timer.

Table 17. BODLEVEL Fuse Coding

(1)

BODLEVEL 2:0 Fuses

Min V

BOT

Typ V

BOT

Max V

BOT

Units

BOD Disabled

1.8

2.7

4.3

Table 18. Brown-out Characteristics

Symbol

Parameter

Min

Typ

Max

Units

HYST

Brown-out Detector Hysteresis

tBOD

Min Pulse Width on Brown-out Reset

µs

VCC

RESET

TIME-OUT

INTERNAL

RESET

VBOT-

VBOT+

tTOUT

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