49
4317K–AVR–03/2013
AT90PWM2/3/2B/3B
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 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
Voltage.
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 (VBOT- in Figure 9-5), the Brown-out Reset is immediately activated. When V
CC increases above the trigger level
(V
BOT+ in Figure 9-5), the delay counter starts the MCU after the Time-out period tTOUT 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
Figure 9-5.
Brown-out Reset During Operation
9.0.6
Watchdog Reset
When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On
the falling edge of this pulse, the delay timer starts counting the Time-out period t
TOUT. Refer to
page 52 for details on operation of the Watchdog Timer.
010
4.2
V
001
2.8
V
000
2.6
V
Table 9-3.
Brown-out Characteristic
sSymbol
Parameter
Min.
Typ.
Max.
Units
V
HYST
Brown-out Detector Hysteresis
70
mV
tBOD
Min Pulse Width on Brown-out Reset
2
s
Table 9-2.
BODLEVEL Fuse Coding
(1)(2)
BODLEVEL 2..0 Fuses
Min VBOT
Typ VBOT
Max VBOT
Units
VCC
RESET
TIME-OUT
INTERNAL
RESET
VBOT-
VBOT+
tTOUT