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ICL7665

CMOS Micropower Over/Under Voltage Detector

Intersil 

ICL7665S

274kΩ

R21A

+5V

+15V

1.02MΩ

R21B

V+

HYST1 HYST2

R21

49.9kΩ

R11

VSET1 VSET2

OUT1 OUT2

+5V

22

100kΩ

MΩ

301 787

kΩ kΩ +5V

-5V

-15V

1

MΩ

POWER

OK

FIGURE 13. MULTIPLE SUPPLY FAULT MONITOR

Combination Low Battery Warning and Low

Battery Disconnect

When using rechargeable batteries in a system, it is

important to keep the batteries from being overdischarged.

The circuit shown in Figure 14 provides a low battery

warning and also disconnects the low battery from the rest of

the system to prevent damage to the battery. OUT1 is used

to shutdown the ICL7663S when the battery voltage drops to

the value where the load should be disconnected. As long as

VSET1 is greater than 1.3V, OUT1 is low, but when VSET1

drops below 1.3V, OUT1 goes high shutting off the

ICL7663S. OUT2 is used for low battery warning. When

VSET2 is greater than 1.3V, OUT2 is high and the low battery

warning is on. When VSET2 drops below 1.3V, OUT2 is low

and the low battery warning goes off. The trip voltage for low

battery warning can be set higher than the trip voltage for

shutdown to give advance low battery warning before the

battery is disconnected.

Power Fail Warning and Powerup/Powerdown

Reset

Figure 15 shows a power fail warning circuit with

powerup/powerdown reset. When the unregulated DC input

is above the trip point, OUT1 is low. When the DC input

drops below the trip point, OUT1 shuts OFF and the power

fail warning goes high. The voltage on the input of the 7805

will continue to provide 5V out at 1A until VIN is less than

7.3V, this circuit will provide a certain amount of warning

before the 5V output begins to drop.

The ICL7665S OUT2 is used to prevent a microprocessor

from writing spurious data to a CMOS battery backup

memory by causing OUT2 to go low when the 7805 5V

output drops below the ICL7665S trip point.

R31

R32

+5V

100Ω

1A

V+

1MΩ

HYST1

HYST2

V+

OUT1

OUT2

+ R21

-

R11

ICL7665S

SET1

SET2

OUT1 GND OUT2

R22

R12

V+

1MΩ

ICL7663S SENSE

SHUTDOWN

GND

VSET

LOW BATTERY SHUTDOWN

LOW BATTERY WARNING

FIGURE 14. LOW BATTERY WARNING AND LOW BATTERY DISCONNECT

3-70

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