Datasheet

LTC2919
9
2919f
If the user’s application requires, the SEL pin may be driven
using a three-state buffer which satisfi es the V
IL
, V
IH
and
leakage conditions of this three-state input pin.
If the state of the SEL pin confi gures a given input as
“negative polarity,” the voltage at that ADJ pin must be
below the trip point (0.5V nominal), or the corresponding
OUT and RST output will be pulled low. Conversely, if a
given input is confi gured as “positive polarity”, the ADJ pin
voltage must be above the trip point or the corresponding
OUT and RST will assert low.
Thus, a “negative polarity” input may be used to deter-
mine 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
APPLICATIO S I FOR ATIO
WUU
U
opposite is true for a “positive polarity” input (–OV or
+UV). These polarity defi nitions 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 confi guration 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 LTC2919 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 confi gurations
for monitoring possible combinations of fault condition
and supply polarity.
ADJ1
ADJ2
OUT1
OUT2
SEL
5V15V
R
P2B
115k
R
P1B
13.7k
R
P1A
11.5k
R
P2A
309k
REF
SEL = V
CC
2 Positive UV
ADJ1
ADJ2
OUT1
OUT2
SEL
5V15V
R
P2B
133k
R
P1B
13.7k
R
P1A
20k
R
P2A
619k
REF
2 Positive OV
ADJ1
ADJ2
OUT1
OUT2
SEL
–5V–15V
R
N2B
137k
R
N1B
13.3k
R
N1A
10.7k
R
N2A
309k
REF
2 Negative UV
SEL = GND
ADJ1
ADJ2
OUT1
OUT2
SEL
–5V–15V
R
N2B
137k
R
N1B
11.8k
R
N1A
30.9k
R
N2A
1.02M
REF
2 Negative OV
ADJ1
ADJ2
OUT1
OUT2
SEL
–15V15V
R
N2
1.02M
R
N1
30.9k
R
P1
11.5k
R
P2
309k
REF
1 Positive UV, 1 Negative OV
ADJ1
ADJ2
OUT1
OUT2
OV (15V)
UV (–15V)
OV (15V)
0V (5V)
UV (–15V)
UV (–5V)
UV (15V)
UV (5V)
OV (–15V)
OV (–5V)
UV (15V)
OV (–15V)
SEL
–15V15V
R
N2
309k
R
N1
10.7k
R
P1
20k
R
P2
619k
REF
1 Positive OV, 1 Negative UV
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, OUT1 and OUT2. Output Pull-up Resistors are Omitted for Clarity.