5347
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 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
connected between V
DD
and V
SS
. The
sensitivity can be externally adjusted to the
individual characteristics of the ionization
chamber by connecting a resistor between
pin 13 and V
DD
, or between pin 13 and V
SS
.
Low Battery.
The low battery threshold is
set internally by a voltage divider connected
between V
DD
and V
SS
. The threshold can be
increased by connecting a resistor between
pin 3 and V
DD
. The threshold can be de-
creased by connecting a resistor between
pin 3 and V
SS
. The battery voltage level is
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.
TYPICAL APPLICATION
NOTE 4
50 kΩ
9V
TIMER
MODE
200 kΩ
200 kΩ
TO
OTHER
UNITS
1
200
Ω
2
NOTE
3
330
Ω
5
6
8.2 MΩ
7
1
µF
8
V
SS
V
DD
3
4
LOGIC
16
15
14
OSC. &
TIMING
13
12
11
10
9
0.1
µF
PUSH
TO
TEST
NOTE
1
HORN
DRIVER
1 MΩ
200 kΩ
0.001
µF
NOTE 2
Dwg. EC-005-2
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.
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
during power up, then reducing V
DD
and monitoring HORN
1
(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.
ALLEGRO [ ALLEGRO MICROSYSTEMS ]
