Datasheet
LTC2919
10
2919f
APPLICATIO S I FOR ATIO
WUU
U
Adjust Input Trip Point
The trip threshold for the supplies monitored by the
adjustable 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 monitoring
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.
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, OUT1 and OUT2. Output Pull-up Resistors are Omitted for Clarity.
ADJ1
ADJ2
OUT1
OUT2
UV
OV
SEL
15V
R
P6
2.37M
R
P5
10.7k
R
P4
76.8k
REF
SEL OPEN
1 Positive UV and OV
ADJ1
ADJ2
OUT1
OUT2
UV (15V)
OV (5V)
SEL
5V15V
R
P2B
133k
R
P1B
13.7k
R
P1A
11.5k
R
P2A
309k
REF
1 Positive UV, 1 Positive OV
1 Negative OV, 1 Positive OV
ADJ1
ADJ2
OUT1
OUT2
OV
UV
SEL
–15V
R
N6
1.02M
R
N4
30.9k
R
N5
4.02k
REF
1 Negative UV and OV
ADJ1
ADJ2
OUT1
OUT2
OV (–15V)
OV (15V)
SEL
15V–15V
R
P2
619k
R
P1
20k
R
N1
30.9k
R
N2
1.02M
REF
ADJ1
ADJ2
OUT1
OUT2
OV (–15V)
UV (–5V)
SEL
–5V–15V
R
N2B
137k
R
N1B
13.3k
R
N1A
30.9k
R
N2A
1.02M
REF
ADJ1
ADJ2
OUT1
OUT2
UV (15V)
UV (–15V)
SEL
–15V15V
R
N2
309k
R
N1
10.7k
R
P1
11.5k
R
P2
309k
REF
1 Positive UV, 1 Negative UV
1 Negative UV, 1 Negative OV
To prevent nuisance resets, the supervisor threshold must
be guaranteed to lie outside the power supply tolerance
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 specifi cation.
All three of the LTC2919 inputs (ADJ1, ADJ2, V
CC
UVLO)
have the same maximum threshold accuracy of ±1.5% of
the programmed nominal input voltage (over the full operat-
ing temperature range). Therefore, using the LTC2919, 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