TYPICAL APPLICATION

Alarm Circuitry. If smoke is detected, the

oscillator period changes to 40 ms and the

horn is enabled. The horn output is typically

160 ms ON, 80 ms OFF. During the OFF

time, smoke is again checked and will inhibit

further alarm output if smoke is not sensed.

During smoke conditions the low battery

alarm is inhibited and the LED is driven at a

1 Hz rate.

Sensitivity Adjust. The detector sensitivity

to smoke is set internally by a voltage divider

sensitivity can be externally adjusted to the

individual characteristics of the ionization

chamber by connecting a resistor between

Low Battery. The low battery threshold is

set internally by a voltage divider connected

increased by connecting a resistor between

creased by connecting a resistor between

checked every 40 seconds during the 10 mA,

10 ms LED pulse. If an LED is not used, it

should be replaced with an equivalent

resistor (typically 500

Ω to 1000 Ω) such that

the battery loading remains at 10 mA.

Timer. An internal timer is provided that can

be used in various configurations to allow for

a period of reduced smoke detector sensitiv-

ity (“hush”). When a high-to-low transition

occurs at pin 1, the internal timer is reset,

the timer mode enabled, and the circuit reset

to a no alarm condition. The LED will flash

at a 10 second rate. If the level of smoke is

increased such that the reduced sensitivity

level is reached, the device will go into the

alarm condition. The timer, however, will

continue to completion of the nominal 10-1/4

minute period (368 clock cycles). If the timer

mode is not used, pin 1 should be tied low.

I/O. A connection is provided at pin 2 to allow multiple smoke detec-

tors to be commoned. If any single unit detects smoke (I/O is driven

high), all connected units will sound their associated horns after a

nominal 3 second delay. The LED is suppressed when an alarm is

signaled from an interconnected unit.

Testing. On power up, all internal counters are reset. Internal test

circuitry allows for low battery check by holding pins 8 and 12 low

All functional tests can be accelerated by driving pin 12 with a 2 kHz

square wave. The 10 ms strobe period must be maintained for proper

operation of the comparator circuitry.

TIMER

MODE

TO

OTHER

UNITS

NOTE

1

NOTE

3

1

2

3

4

5

6

7

89

10

11

12

13

14

15

16

LOGIC

OSC. &

TIMING

HORN

DRIVER

Dwg. EC-005-2

9 V

NOTE 2

200 k

Ω

200

Ω

8.2 M

Ω

1

µF

0.1

µF

PUSH

TO

TEST

0.001

µF

330

Ω

NOTE 4

NOTE 1: Use an external resistor to adjust sensitivity for a particular smoke

chamber.

NOTE 2: Select resistor to reduce sensitivity during timer mode.

NOTE 3: A resistor to ground or V

DD

may be added to this pin to modify low battery

voltage threshold.

NOTE 4: Reverse battery protection must be supplied externally.

5347

SMOKE DETECTOR

with INTERCONNECT

and TIMER