LTC2909 Linear Technology, LTC2909 Datasheet - Page 10

• Manufacturer Part Number: LTC2909
• Description: OV and Negative Voltage Monitor
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
LTC2909
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
10
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
3.09M
115k
3.09M
R
R
R
R
115k
15V (UV)
1 Positive UV, 1 Negative UV
P2
P1
P2A
P1A
1 Positive UV, 1 Positive OV
15V (UV)
2.37M
10.7k
76.8k
15V (UV/OV)
U
R
R
R
P6
P5
P4
1 Positive UV and OV
1.33M
3.09M
R
R
107k
137k
–15V (UV)
R
R
P2B
P1B
5V (OV)
N2
N1
U
ADJ1
ADJ2
REF
ADJ1
ADJ2
REF
ADJ1
ADJ2
REF
SEL
W
SEL
SEL
U
SEL OPEN
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 LTC2909 inputs (ADJ1, ADJ2, V
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.
40.2k
R
N5
10.2M
R
R
10.2M
309k
–15V (OV)
N2A
N1A
309k
309k
1 Negative UV, 1 Negative OV
R
R
R
1 Negative OV, 1 Positive OV
–15V (OV)
N4
N2
N1
1 Negative UV and OV
10.2M
6.19M
1.37M
–15V (UV/OV)
R
R
200k
133k
R
R
R
N2B
N1B
–5V (UV)
15V (OV)
N6
P2
P1
ADJ1
ADJ2
REF
ADJ1
ADJ2
REF
ADJ1
ADJ2
REF
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SEL
SEL
SEL
CC
UVLO)
2909fa