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
Table 2b. 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 OPEN
15V (UV/OV)
RP6
2.37M
RP5
10.7k
RP4
76.8k
ADJ1
ADJ2 SEL
REF
–15V (UV/OV)
RN5
40.2k
RN6
10.2M
RN4
309k
ADJ1
ADJ2 SEL
REF
1 Positive UV and OV
15V (UV) –15V (UV)
RP2
3.09M
RN2
3.09M
ADJ1
RP1
115k
RN1
107k
ADJ2 SEL
REF
1 Negative UV and OV
–15V (OV) 15V (OV)
RN2
RP2
10.2M 6.19M
ADJ1
RN1
309k
RP1
200k
ADJ2 SEL
REF
1 Positive UV, 1 Negative UV
15V (UV) 5V (OV)
RP2A RP2B
3.09M 1.33M
ADJ1
RP1A
115k
RP1B
137k
ADJ2 SEL
REF
1 Positive UV, 1 Positive OV
1 Negative OV, 1 Positive OV
–15V (OV) –5V (UV)
RN2A
10.2M
RN2B
1.37M
ADJ1
RN1A
309k
RN1B
133k
ADJ2 SEL
REF
1 Negative UV, 1 Negative OV
Adjust Input Trip Point
The trip threshold for the supplies monitored by the adjust-
able inputs is set with an external resistor divider, allowing
the user complete control over the trip point. Selection of
this trip voltage is crucial to the reliability of the system.
Any power supply has some tolerance band within which
it is expected to operate (e.g., 5V ±10%). It is generally
undesirable that a supervisor issue a reset when the power
supply is inside this tolerance band. Such a “nuisance”
reset reduces reliability by preventing the system from
functioning under normal conditions.
To prevent nuisance resets, the supervisor threshold must
be guaranteed to lie outside the power supply tolerance
10
band. To ensure that the threshold lies outside the power
supply tolerance range, the nominal threshold must lie out-
side that range by the monitor’s accuracy specification.
All three of the LTC2909 inputs (ADJ1, ADJ2, VCC UVLO)
have the same relative threshold accuracy of ±1.5% of the
programmed nominal input voltage (over the full operating
temperature range). Therefore, using the LTC2909, the
typical 10% UV threshold is at 11.5% below the nominal
input voltage level. For a 5V input, the threshold is nominally
4.425V. With ±1.5% accuracy, the trip threshold range is
4.425V ±75mV over temperature (i.e., 10% to 13% below
5V). The monitored system must thus operate reliably
down to 4.35V or 13% below 5V over temperature.
2909fb
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