Texas Instruments TPS3801, Отчет о приложении

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Voltage Supervision at the V
DD
Terminal
6 SLVA075
3 Voltage Supervision at the V
DD
Terminal
3.1 Functional Description
The main function of an SVS is to supervise a supply voltage and to trigger a reset
signal if necessary.
If the supply voltage falls below the negative-going threshold voltage V
IT–
, the
device has to assert a reset. The reset returns to the inactive state, about 200 ms
after the voltage again exceeds the positive-going threshold voltage V
IT+
. This
delay time t
d
of 200 ms is necessary to ensure that the crystal oscillator works
stable after a power-on reset and that the processor initialization could be
completed.
The difference between the negative-going and the positive-going threshold
voltage is called hysteresis V
hys
:
V
IT
)
+
V
I
T–
)
V
hys
The reason for the hysteresis is to avoid toggling of the reset output if the voltage
is noisy.
For a better understanding, a timing diagram with these parameters is given:
RESET Goes High After Delay
Time of Typical 200 ms
RESET Goes Low
VSENSE
VCC
VIT+
VIT–
t
Vhys
Figure 6. Relations Between V
IT+
, V
IT–
, and V
hys
The devices are specified in a temperature range of –40
°
C to +85
°
C and for an
input voltage range of 2 V to 6 V. Due to the wide range of temperature and input
voltage and because of process variations the threshold voltages vary a little. The
minimum, typical and maximum values of the negative-going threshold voltages
and the typical hysteresis can be taken from Table 4.
(1)