Rainbow-electronics ATmega3290P_V Manual de usuario descargar pdf (Pagina 43)

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+

= V

BOT

+ V

HYST

/2 and V

BOT-

= V

BOT

- V

HYST

/2.

Note: 1. V

BOT

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

devices where this is the case, the device is tested down to V

= V

BOT

during the

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

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

decreases to a value below the trigger level (V

BOT-

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

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

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

11 BOD Disabled

10 1.8

V01 2.7

00 4.3

Table 18. Brown-out Characteristics

Symbol Parameter Min Typ Max Units

HYST

Brown-out Detector Hysteresis 50 mV

BOD

Min Pulse Width on Brown-out Reset 2 µs

RESET

TIME-OUT

INTERNAL

RESET

BOT-

BOT+

TOUT

1 2 ... 38 39 40 41 42 43 44 45 46 47 48 ... 374 375

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