LTC2919 データシートの表示（PDF） - Analog Devices

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LTC2919

Precision Triple/Dual Input UV, OV and Negative Voltage Monitor

Analog Devices 

LTC2919

APPLICATIONS INFORMATION

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.

SEL OPEN

15V

RP6

2.37M

RP5

10.7k

RP4

76.8k

ADJ1 OUT1 UV

ADJ2 OUT2 OV

REF SEL

RN5

4.02k

–15V

RN6

1.02M

RN4

30.9k

ADJ1 OUT1 OV

ADJ2 OUT2 UV

REF SEL

1 Positive UV and OV

15V

RP2

309k

–15V

RN2

309k

ADJ1 OUT1 UV (15V)

RP1

11.5k

RN1

10.7k

ADJ2 OUT2 UV (–15V)

REF SEL

1 Negative UV and OV

–15V 15V

RN2

1.02M

RP2

619k

ADJ1 OUT1 OV (–15V)

RN1

RP1

30.9k

20k

ADJ2 OUT2 OV (15V)

REF SEL

1 Positive UV, 1 Negative UV

15V

5V

RP2A

309k

RP2B

133k

ADJ1 OUT1 UV (15V)

RP1A

11.5k

RP1B

13.7k

ADJ2 OUT2 OV (5V)

REF SEL

1 Positive UV, 1 Positive OV

1 Negative OV, 1 Positive OV

–15V

–5V

RN2A

1.02M

RN2B

137k

ADJ1 OUT1 OV (–15V)

RN1A

30.9k

RN1B

13.3k

ADJ2 OUT2 UV (–5V)

REF SEL

1 Negative UV, 1 Negative OV

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 gener-

ally undesirable that a supervisor issue a reset when the

power supply is inside this tolerance band. Such a “nui-

sance” 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

band. To ensure that the threshold lies outside the power

supply tolerance range, the nominal threshold must lie

outside that range by the monitor’s accuracy specification.

All three of the LTC2919 inputs (ADJ1, ADJ2, VCC UVLO)

have the same maximum threshold accuracy of ±1.5%

of the programmed nominal input voltage (over the

full operating 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 thresh-

old is nominally 4.425V. With ±1.5% accuracy, the trip

For more information www.analog.com

Rev. A

11

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