Rainbow-electronics ATmega64C1 Manual do Utilizador descarregar pdf (Página 47)

7647A–AVR–02/08

ATmega32/64/M1/C1

7.2.3 Brown-out Detection

ATmega32/64/M1/C1 has an On-chip Brown-out Detection (BOD) circuit for monitoring the V

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+

BOT

+ V

HYST

/2 and V

BOT-

= V

BOT

- V

HYST

/2.

Notes: 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 guar-

antees 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 = 010 for Low Operating Voltage and BODLEVEL = 101 for High Operating Volt-

age .

2. Values are guidelines only.

Notes: 1. Values are guidelines only.

When the BOD is enabled, and V

decreases to a value below the trigger level (V

BOT-

in Figure

7-5), the Brown-out Reset is immediately activated. When V

increases above the trigger level

BOT+

in Figure 7-5), 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 7-3.

Table 7-2. BODLEVEL Fuse Coding

(1)(2)

BODLEVEL 2..0 Fuses Min V

BOT

Typ V

BOT

Max V

BOT

Units

111 2.6

110

RESERVED101

100

011 4.3 V

010 2.7 V

001 4.5 V

000 DISABLED

Table 7-3. Brown-out Characteristics

(1)

Symbol Parameter Min. Typ. Max. Units

HYST

Brown-out Detector Hysteresis 50 mV

BOD

Min Pulse Width on Brown-out Reset 2 µs

1 2 ... 42 43 44 45 46 47 48 49 50 51 52 ... 365 366

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