Datasheet

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 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
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 (V
BOT-
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 t
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
BOD
given in Table 9-3.
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 Characteristics
(1)
Symbol Parameter Min. Typ. Max. Units
V
HYST
Brown-out Detector Hysteresis 70 mV
t
BOD
Min Pulse Width on Brown-out Reset 2 µs
Table 9-2. BODLEVEL Fuse Coding
(1)(2)
BODLEVEL 2..0 Fuses Min V
BOT
Typ V
BOT
Max V
BOT
Units
V
CC
RESET
TIME-OUT
INTERNAL
RESET
V
BOT-
V
BOT+
t
TOUT