AT90USB82/162
9.5
Brown-out Detection
AT90USB82/162 has an On-chip Brown-out Detection (BOD) circuit for monitoring the VCC 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 VBOT+
BOT + VHYST/2 and VBOT- = VBOT - VHYST/2.
=
V
Table 9-2.
BODLEVEL Fuse Coding(1)
BODLEVEL 2..0 Fuses Min VBOT
Typ VBOT
Max VBOT
Units
111
110
101
100
011
010
001
000
BOD Disabled
2.5
2.7
2.8
3.3
3.4
3.8
4.1
2.7
2.9
3.0
3.5
3.6
4.0
4.3
2.9
3.1
3.2
3.7
3.8
4.2
4.5
V
Note:
1. VBOT may be below nominal minimum operating voltage for some devices. For devices where
this is the case, the device is tested down to VCC = VBOT during the production test. This guar-
antees that a Brown-Out Reset will occur before VCC drops to a voltage where correct
operation of the microcontroller is no longer guaranteed. The test is performed using
BODLEVEL = 110 for AT90USB82/162 and BODLEVEL = 101 for AT90USB82/162L.
Table 9-3.
Symbol
VHYST
Brown-out Characteristics
Parameter
Min
Typ
50
2
Max
Units
mV
Brown-out Detector Hysteresis
Min Pulse Width on Brown-out Reset
tBOD
ns
When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in Figure
9-5), the Brown-out Reset is immediately activated. When VCC increases above the trigger level
(VBOT+ in Figure 9-5), the delay counter starts the MCU after the Time-out period tTOUT has
expired.
The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level for
longer than tBOD given in Table 9-1.
49
7707D–AVR–07/08
ATMEL [ ATMEL ]
