imp813 ETC-unknow, imp813 Datasheet - Page 7

• Manufacturer Part Number: imp813
• Description: Low-power Supervisor Circuits
• Manufacturer: ETC-unknow

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Monitoring Voltages Other Than V
The IMP705-708 can monitor voltages other than V
Power Fail circuitry. If a resistive divider is connected from the
voltage to be monitored to the Power Fail input, PFI, the PFO
(output) will go LOW if the divider voltage goes below its 1.25V
reference. Should hysteresis be desired, connect a resistor (equal
to approximately 10 times the sum of the two resistors in the
divider) between the PFI and PFO pins. A capacitor between PFI
and GND will reduce circuit sensitivity to input high-frequency
noise. If it is desired to assert a RESET in addition to the PFO flag,
this may be achieved by connecting the PFO output to MR.
1999 IMP, Inc.
Figure 4. Monitoring Voltages Other Than V
V
IN
= 12V
1M
130k
9
9
PFI
IMP70x
GND
V
CC
RESET
V
CC
PFO
MR
= 5V
12V Threshold
~10.87V
CC
To Processor
408-432-9100/www.impweb.com
CC
705_07.eps
CC
using the
Monitoring a Negative Voltage
The Power-Fail circuitry can also monitor a negative supply rail.
When the negative rail is OK, PFO will be LOW, and when the
negative rail is failing (not negative enough), PFO goes HIGH
(the opposite of when positive voltages are monitored). To trigger
a reset, these outputs need to be inverted: adding the resistors
and transistor as shown achieves this. The RESET output will
then have the same sense as for positive voltages: good = HIGH,
bad = LOW. It should be noted that this circuit’s accuracy depends
on the V
CC
+5V
—
Figure 5. Monitoring a Negative Voltage
+
line, the PFI threshold tolerance, and the resistors.
Negative Input
Voltage
RP
RN
IMP705/6/7/8, 8
IMP705/6/7/8, 8
PFI
IMP70x
Application Information
GND
V
CC
RESET
PFO
MR
5 1 25
−
RP
.
=
1 25
.
RN
−
705_09.eps
1
1
V
TRIP
3L
3L
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