
53
7734Q–AVR–02/12
AT90PWM81/161
7.1.5
Brown-out Detection
AT90PWM81/161 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+ = VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.
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 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 Voltageand BODLEVEL = 101 for High Operating
Voltage.
2. Values are guidelines only.
Notes:
1. Values are guidelines only.
When V
Brown-out Reset is immediately activated. When V
CC increases above the trigger level (VBOT+ in
TOUT has
expired.
The BOD circuit will only detect a drop in V
CC if the voltage stays below the trigger level for lon-
ger than t
Table 7-2.
BODLEVEL fuse coding
BODLEVEL 2..0 fuses
Min VBOT
Typ VBOT
Max VBOT
Units
111
Forbidden, BOD must be enabled
110
1.8
V
101 (default configuration)
2.7
100
3.9
4.3
4.6
011
2.3
010
2.2
001
1.9
000
2.5
2.0
2.9
Table 7-3.
Brown-out characteristics
(1).
Symbol
Parameter
Minimum
Typical
Maximum
Units
VHYST
Brown-out detector hysteresis
70
mV
t
BOD
Minimum pulse width on brown-out reset
2
s