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A5349

AC SMOKE DETECTOR WITH INTERCONNECT AND TIMER

Allegro MicroSystems 

5349

AC SMOKE DETECTOR

with INTERCONNECT

and TIMER

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-supply

alarm is inhibited.

LED. The LED is continuously ON during the

standby mode indicating the unit is receiving

power. During a remote alarm condition the

LED remains ON. The LED is OFF during a

local alarm condition.

Sensitivity Adjust. The detector sensitivity

to smoke is set internally by a voltage divider

connected between VDD and VSS. The

sensitivity can be externally adjusted to the

individual characteristics of the ionization

chamber by connecting a resistor between

pin 13 and VDD, or between pin 13 and VSS.

Low Supply. The low supply threshold is set

internally by a voltage divider connected

between VDD and VSS. The threshold can be

increased by connecting a resistor between

pin 3 and VDD. The threshold can be de-

creased by connecting a resistor between pin

3 and VSS. The supply voltage level is

checked every 40 seconds.

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 in-

creased 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 detectors to be

commoned. If any single unit detects smoke

(I/O is driven high), all connected units will

TYPICAL APPLICATION

+ SUPPLY

TIMER

MODE

200 kΩ

TO

1

OTHER

UNITS

200 Ω

2

NOTE

3

3

4

330 Ω

5

16

LOGIC

15

14

OSC. &

13

TIMING

12

8.2 MΩ

6 V DD

HORN

DRIVER

11

7

10

1 µF

8

VSS 9

0.1 µF

PUSH

TO

TEST

NOTE

1

NOTE 2

0.001 µF

Dwg. EC-005-1A

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 VDD may be added to this pin to modify low battery

voltage threshold.

NOTE 4: Reverse supply protection must be supplied externally.

sound their associated horns after a nominal 3 second delay. The LED

remains ON when an alarm is signaled from an interconnected unit

and a local smoke condition does not exist.

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

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

during power up, then reducing VDD and monitoring HORN1 (pin 10).

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.

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