AT90USB64/128
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 8-2.
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
2.0
2.2
2.4
2.6
3.4
3.5
4.3
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 AT90USB64/128 and BODLEVEL = 101 for AT90USB64/128L.
Table 8-3.
Symbol
VHYST
Brown-out Characteristics
Parameter
Min
Typ
Max
Units
mV
Brown-out Detector Hysteresis
Min Pulse Width on Brown-out Reset
50
tBOD
ns
When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in Figure
8-5), the Brown-out Reset is immediately activated. When VCC increases above the trigger level
(VBOT+ in Figure 8-5), 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 8-1.
Figure 8-5. Brown-out Reset During Operation
VBOT+
VCC
VBOT-
RESET
t
TOUT
TIME-OUT
INTERNAL
RESET
61
7593A–AVR–02/06
ATMEL [ ATMEL ]
