Datasheet

108
XMEGA B [DATASHEET]
8291B–AVR–01/2013
When V
CC
increases above the trigger level (V
BOT+
in Figure 9-4), the reset counter starts the MCU after the timeout
period, t
TOUT
, has expired.
The trigger level has a hysteresis to ensure spike free brownout detection. The hysteresis on the detection level should
be interpreted as V
BOT+
= V
BOT
+ V
HYST
/2 and V
BOT-
= V
BOT
- V
HYST
/2.
The BOD circuit will detect a drop in V
CC
only if the voltage stays below the trigger level for longer than t
BOD
.
Figure 9-4. Brownout detection reset.
For BOD characterization data consult the device datasheet. The programmable BODLEVEL setting is shown in Table 9-
2.
Table 9-2. Programmable BODLEVEL setting.
Notes: 1. The values are nominal values only. For accurate, actual numbers, consult the device datasheet.
2. Changing these fuse bits will have no effect until leaving programming mode.
The BOD circuit has three modes of operation:
 Disabled: In this mode, there is no monitoring of the V
CC
level.
 Enabled: In this mode, the V
CC
level is continuously monitored, and a drop in V
CC
below V
BOT
for a period of t
BOD
will give a brownout reset
 Sampled: In this mode, the BOD circuit will sample the V
CC
level with a period identical to that of the 1kHz output
from the ultra low power (ULP) internal oscillator. Between each sample, the BOD is turned off. This mode will
BOD level Fuse BODLEVEL[2:0]
(2)
V
BOT
(1)
Unit
BOD level 0 111 1.6
V
BOD level 1 110 1.8
BOD level 2 101 2.0
BOD level 3 100 2.2
BOD level 4 011 2.4
BOD level 5 010 2.6
BOD level 6 001 2.8
BOD level 7 000 3.0
V
CC
T
IME-OUT
I
NTERNAL
RESET
V
BOT-
V
BOT+
t
TOUT
t
BOD