LTC2919

9

2919f

If the user’s application requires, the SEL pin may be driven

leakage conditions of this three-state input pin.

If the state of the SEL pin configures 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 configured 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

opposite is true for a “positive polarity” input (–OV or

+UV). These polarity definitions 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 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 configurations

for monitoring possible combinations of fault condition

and supply polarity.

ADJ1

ADJ2

OUT1

OUT2

SEL

5V

15V

115k

13.7k

11.5k

309k

REF

2 Positive UV

ADJ1

ADJ2

OUT1

OUT2

SEL

5V

15V

133k

13.7k

20k

619k

REF

2 Positive OV

ADJ1

ADJ2

OUT1

OUT2

SEL

–5V

–15V

137k

13.3k

10.7k

309k

REF

2 Negative UV

SEL = GND

ADJ1

ADJ2

OUT1

OUT2

SEL

–5V

–15V

137k

11.8k

30.9k

1.02M

REF

2 Negative OV

ADJ1

ADJ2

OUT1

OUT2

SEL

–15V

15V

1.02M

30.9k

11.5k

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

–15V

15V

309k

10.7k

20k

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.