Microprocessor Voltage Monitor with

Dual Over/Undervoltage Detection

ICL7665

OUT2

OUT1

SET1

SET2

HYST2

HYST1

R31

22M

22M

100k

POWER OK

301k

R11

49.9k

V+

+5V

-5V

-15V

787k

+5V

+15V

R21A

274k

R21B

1.02M

+5V

HYST1

SET1

HYST2

SET2

GND

OUT2

V+

V+

OUT1

OUT2

SHDN

SENSE

ICL7663

ICL7665

GND

LOW-BATTERY WARNING

LOW-BATTERY SHUTDOWN

+5V, 1A

OUTPUT

R31

OUT1

SET

R21

R11

R32

R22

R12

1M

100

Ω

Figure 8. Low-Battery Warning and Low-Battery Disconnect

Figure 7. Multiple-Supply Fault Monitor

HYST1

SET1

HYST2

SET2

ICL7665

V+

UNREGULATED

DC INPUT

BACK-UP

BATTERY

RESET

OR

WRITE

ENABLE

POWER-FAIL WARNING

4700µF

470µF

2.2M

1M

5.6M

715k

130k

22M

OUT2

OUT1

5V, 1A

OUTPUT

7805

5V REGULATOR

HYST1

SET1

HYST2

SET2

OUT1

OUT2

ICL7665

V+

7805

5V REGULATOR

10VAC

60Hz

20V CENTER

TAPPED TRANS

4700

µF

R2

1M

681k

Q1

R3

1M

C1

R1

+5V

POWER-FAIL

WARNING

100k

5V, 1A

Figure 9. Power-Fail Warning and Power-Up/Power-Down Reset

Figure 10. AC Power-Fail and Brownout Detector

ICL7665

OUT1

OUT2

SET2

SET1

+5V SUPPLY

HYST1

HYST2

V+

13M

5%

7.5M

5%

249k

324k

100k

100k

OVERVOLTAGE

DETECTOR

UNDERVOLTAGE

DETECTOR

POWER OK

Figure 6. Fault Monitor for a Single Supply

10

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