ATmega16/32/64/M1/C1
7.2.3
Brown-out Detection
ATmega16/32/64/M1/C1 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 VBOT+
BOT + VHYST/2 and VBOT- = VBOT - VHYST/2.
V
=
V
Table 7-2.
BODLEVEL Fuse Coding(1)(2)
BODLEVEL 2..0 Fuses
Typ VBOT
Disabled
4.5
Units
111
110
011
100
010
001
101
000
V
V
V
V
V
V
V
4.4
4.3
4.2
2.8
2.7
2.6
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 guar-
antees that a Brown-Out Reset will occur before VCC 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.
Table 7-3.
Symbol
VHYST
Brown-out Characteristics(1)
Parameter
Min.
Typ.
80
2
Max.
Units
mV
Brown-out Detector Hysteresis
Min Pulse Width on Brown-out Reset
tBOD
µs
Notes: 1. Values are guidelines only.
When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in Figure
7-5 on page 50), the Brown-out Reset is immediately activated. When VCC increases above the
trigger level (VBOT+ in Figure 7-5 on page 50), the delay counter starts the MCU after the
Time-out period tTOUT has expired.
The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level for lon-
ger than tBOD given in Table 7-3.
49
7647F–AVR–04/09
ATMEL [ ATMEL ]
