Datasheet

39
2586D–AVR–02/06
ATtiny25/45/85
Note: 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.
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
longer than t
BOD
given in Table 9-1.
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 41 for details on operation of the Watchdog Timer.
110 1.8
V
101 2.7
100 4.3
011 2.3
010 2.2
001 1.9
000 2.0
Table 9-3. 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
Table 9-2. BODLEVEL Fuse Coding
(1)
BODLEVEL [2:0] Fuses Min V
BOT
Typ V
BOT
Max V
BOT
Units
V
CC
RESET
TIME-OUT
I
NTERNAL
RESET
V
BOT-
V
BOT+
t
TOUT