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System Reset and Initialization
2-4
System Resets, Interrupts, and Operating Modes
2.1.2 Brownout Reset (BOR)
Some devices have a brownout reset circuit (see device-specific datasheet)
that replaces the POR detect and POR delay circuits. The brownout reset
circuit detects low supply voltages such as when a supply voltage is applied
to or removed from the V
CC
terminal. The brownout reset circuit resets the
device by triggering a POR signal when power is applied or removed. The
operating levels are shown in Figure 2−3.
The POR signal becomes active when V
CC
crosses the V
CC(start)
level. It
remains active until V
CC
crosses the V
(B_IT+)
threshold and the delay t
(BOR)
elapses. The delay t
(BOR)
is adaptive being longer for a slow ramping V
CC.
The
hysteresis V
hys(B_ IT−)
ensures that the supply voltage must drop below
V
(B_IT−)
to generate another POR signal from the brownout reset circuitry.
Figure 2−3. Brownout Timing
t
(BOR)
V
CC(start)
V
CC
V
(B_IT−)
Set Signal for
POR circuitry
V
(B_IT+)
V
hys(B_IT−)
As the V
(B_IT−)
level is significantly above the V
min
level of the POR circuit, the
BOR provides a reset for power failures where V
CC
does not fall below V
min.
See device-specific datasheet for parameters.