LTC2909 データシートの表示（PDF） - Linear Technology
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LTC2909 Datasheet PDF : 16 Pages
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LTC2909
APPLICATIO S I FOR ATIO
If the state of the SEL pin configures a given input as
“negative polarity,” the voltage at the ADJx pin must be
below the trip point (0.5V nominal), or the ⎯R⎯S⎯T output will
be pulled low. Conversely, if a given input is configured
as “positive polarity,” the pin voltage must be above the
trip point or ⎯R⎯S⎯T will assert low.
Thus, a “negative polarity” input may be used to determine
whether a monitored negative voltage is smaller in absolute
value than it should be (–UV), or a monitored positive
voltage is larger than it should be (+OV). The opposite is
true for a “positive polarity” input (–OV or +UV). These
usages are also shown in Table 1. For purposes of this
data sheet, a negative voltage is considered “undervoltage”
if it is closer to ground than it should be (e.g., –4.3V for
a –5V supply).
Proper configuration of the SEL pin and setting of the
trip-points via external resistors allows for any two fault
conditions to be detected. For example, the LTC2909 may
monitor two supplies (positive, negative or one of each)
for UV or for OV (or one UV and one OV). It may also
monitor a single supply (positive or negative) for both UV
and OV. Tables 2a and 2b show example configurations
for monitoring possible combinations of fault condition
and supply polarity.
Table 2a. Possible Combinations of Supply Monitoring. For Example Purposes, All Supplies are Monitored at 5% Tolerance and
Connections are Shown Only for ADJ1, ADJ2, REF, SEL
SEL = VCC
SEL = GND
15V (UV) 5V (UV)
RP2A RP2B
3.09M 1.15M
ADJ1
–15V (UV) –5V (UV)
RN2A
3.09M
RN2B
1.37M
ADJ1
RP1A
115k
RP1B
137k
ADJ2 SEL
REF
RN1A
107k
RN1B
133k
ADJ2 SEL
REF
2 Positive UV
2 Negative UV
–15V (OV) –5V (OV)
RN2A
10.2M
RN2B
1.37M
ADJ1
RN1A
309k
RN1B
118k
ADJ2 SEL
REF
15V (OV) 5V (OV)
RP2A RP2B
6.19M 1.33M
ADJ1
RP1A
200k
RP1B
137k
ADJ2 SEL
REF
2 Negative OV
15V (UV) –15V (OV)
RP2
3.09M
RN2
10.2M
ADJ1
RP1
115k
RN1
309k
ADJ2 SEL
REF
2 Positive OV
15V (OV) –15V (UV)
RP2
RN2
6.19M 3.09M
ADJ1
RP1
200k
RN1
107k
ADJ2 SEL
REF
1 Positive UV, 1 Negative OV
1 Positive OV, 1 Negative UV
2909fb
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