ICL7665SCBAZ datasheet(11/14 Pages) INTERSIL

11 / 14 page

FN3182.8

April 5, 2006

Simple High/Low Temperature Alarm

Figure 16 illustrates a simple high/low temperature alarm

which uses the ICL7665S with an NPN transistor. The

voltage at the top of R1 is determined by the VBE of the

transistor and the position of R1’s wiper arm. This voltage

has a negative temperature coefficient. R1 is adjusted so

that VSET2 equals 1.3V when the NPN transistor’s

temperature reaches the temperature selected for the high

temperature alarm. When this occurs, OUT2 goes low. R2 is

adjusted so that VSET1 equals 1.3V when the NPN

transistor’s temperature reaches the temperature selected

for the low temperature alarm. When the temperature drops

below this limit, OUT1 goes low.

AC Power Fail and Brownout Detector

Figure 17 shows a circuit that detects AC undervoltage by

monitoring the secondary side of the transformer. The

capacitor, C1, is charged through R1 when OUT1 is OFF.

With a normal 100 VAC input to the transformer, OUT1 will

discharge C1 once every cycle, approximately every 16.7ms.

When the AC input voltage is reduced, OUT1 will stay OFF,

so that C1 does not discharge. When the voltage on C1

reaches 1.3V, OUT2 turns OFF and the power fail warning

goes high. The time constant, R1C1, is chosen such that it

takes longer than 16.7ms to charge C1 1.3V.

HYST1

VSET1

VSET2

HYST2

V+

OUT1

OUT2

5.86k

Ω

130k

Ω

BACKUP

BATTERY

7805

5V REGULATOR

UNREGULATED

DC INPUT

Ω

22M

Ω

2.2M

Ω

715k

Ω

RESET OR

WRITE

ENABLE

POWER

FAIL

WARNING

470

µF

4700

µF

ICL7665S

FIGURE 15. POWER FAIL WARNING AND POWERUP/POWERDOWN RESET

ICL7665S

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