3 brown-out detection – Rainbow Electronics ATmega64C1 User Manual
Page 47
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
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+
=
V
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
CC
= V
BOT
during the production test. This guar-
antees 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 = 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
CC
decreases to a value below the trigger level (V
BOT-
in
), the Brown-out Reset is immediately activated. When V
CC
increases above the trigger level
(V
BOT+
in
), 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
Table 7-2.
BODLEVEL Fuse Coding
BODLEVEL 2..0 Fuses
Min V
BOT
Typ V
BOT
Max V
BOT
Units
111
2.6
110
RESERVED
101
100
011
4.3
V
010
2.7
V
001
4.5
V
000
DISABLED
Table 7-3.
Brown-out Characteristics
Symbol
Parameter
Min.
Typ.
Max.
Units
V
HYST
Brown-out Detector Hysteresis
50
mV
t
BOD
Min Pulse Width on Brown-out Reset
2
µs