Datasheet

52
7766F–AVR–11/10
ATmega16/32U4
8.0.5 Brown-out Detection
ATmega16U4/ATmega32U4 has an On-chip Brown-out Detection (BOD) circuit for monitoring
the V
CC
level during operation by comparing it to a fixed trigger level. The trigger level for the
BOD can be selected by the BODLEVEL Fuses. The trigger level has a hysteresis to ensure
spike free Brown-out 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.
When the BOD is enabled, and V
CC
decreases to a value below the trigger level (V
BOT-
in Figure
8-5), the Brown-out Reset is immediately activated. When V
CC
increases above the trigger level
(V
BOT+
in Figure 8-5), 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 8-1.
Figure 8-5. Brown-out Reset During Operation
Table 8-2. BODLEVEL Fuse Coding
BODLEVEL 2..0 Fuses Min V
BOT
Typ V
BOT
Max V
BOT
Units
111 BOD Disabled
110 1.8 2.0 2.2
V
101 2.0 2.2 2.4
100 2.2 2.4 2.6
011 2.4 2.6 2.8
010 3.2 3.4 3.6
001 3.3 3.5 3.7
000 4.0 4.3 4.5
Table 8-3. 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 ns
V
CC
RESET
TIME-OUT
INTERNAL
RESET
V
BOT-
V
BOT+
t
TOUT