Datasheet

54
7682C–AUTO–04/08
AT90CAN32/64/128
Figure 7-4. External Reset During Operation
7.1.5 Brown-out Detection
AT90CAN32/64/128 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.
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 Volt-
age .
2. Not tested.
CC
Table 7-2. BODLEVEL Fuse Coding
(1)
BODLEVEL 2..0 Fuses Min V
BOT
Typ V
BOT
Max V
BOT
Units
111 BOD Disabled
110 3.8 4.1 4.4 V
101 4.0
(2)
V
100 3.9
(2)
V
011 3.8
(2)
V
010 2.5 2.7 2.9 V
001 2.6
(2)
V
000 2.5
(2)
V
Table 7-3. Brown-out Characteristics
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