Datasheet

42
ATtiny828 [DATASHEET]
8371A–AVR–08/12
Figure 18. Brown-out Reset During Operation
The BOD circuit will not detect a drop in V
CC
unless the voltage stays below the trigger level for the detection time, t
BOD
(see “System and Reset Characteristics” on page 250).
The BOD circuit has three modes of operation:
z Disabled: In this mode of operation V
CC
is not monitored and, hence, it is recommended only for applications
where the power supply remains stable.
z Enabled: In this mode the V
CC
level is continuously monitored. If V
CC
drops below V
BOT
for at least t
BOD
a brown-
out reset will be generated.
z Sampled: In this mode the V
CC
level is sampled on each negative edge of a 1kHz clock that has been derived
from the 32kHz ULP oscillator. Between each sample the BOD is turned off. Compared to the mode where BOD is
constantly enabled this mode of operation reduces power consumption but fails to detect drops in V
CC
between
two positive edges of the 1kHz clock. When a brown-out is detected in this mode, the BOD circuit is set to enabled
mode to ensure that the device is kept in reset until V
CC
has risen above V
BOT
. The BOD will return to sampled
mode after reset has been released and the fuses have been read in.
The BOD mode of operation is selected using BODACT and BODPD fuse bits. The BODACT fuse bits determine how
the BOD operates in active and idle mode, as shown in Table 11.
Table 11. Setting BOD Mode of Operation in Active and Idle Modes
The BODPD fuse bits determine the mode of operation in all sleep modes except idle mode, as shown in Table 12.
BODACT1 BODACT0 Mode of Operation
0 0 Reserved
0 1 Sampled
1 0 Enabled
1 1 Disabled
V
CC
RESET
TIME-OUT
INTERNAL
RESET
V
BOT-
V
BOT+
t
TOUT