5355
SMOKE DETECTOR
WITH INTERCONNECT
NO CONNECT.
I/O
LOW-V SET
NO CONNECT.
LED
+ SUPPLY
TIMING RES.
FEEDBACK
1
2
3
4
5
6
7
8
V
SS
V
DD
NC
NC
LOGIC
16
15
14
13
12
11
10
9
GUARD 2
DETECT. IN
GUARD 1
SENSITIVITY
SET
OSC. CAP.
HORN 2
HORN 1
– SUPPLY
Data Sheet
26110.5A
The A5355CA is a low-current, CMOS circuit providing all of the
required features for an ionization-type smoke detector. A networking
capability allows as many as 125 units to be interconnected so that if
any unit senses smoke, all units will sound an alarm. In addition,
special features are incorporated to facilitate alignment and test of the
finished smoke detector. This device is designed to comply with
Underwriters Laboratories Specification UL217.
The internal oscillator and timing circuitry keeps standby power to
a minimum by powering down the device for 1.66 seconds and sensing
smoke for only 10 ms. Every 24 on/off cycles, a check is made for low
battery condition. By substituting other types of sensors, or a switch
for the ionization detector, this very-low power device can be used in
numerous other battery-operated safety/security applications.
The A5355CA is supplied in a low-cost, 16-pin dual in-line plastic
package. It is rated for continuous operation over the temperature
range of 0°C to +50°C.
OSC. &
TIMING
HORN
DRIVER
Dwg. PC-004-1
FEATURES
s
s
s
s
s
s
Interconnect Up to 125 Detectors
Piezoelectric Horn Driver
Guard Outputs for Detector Input
Pulse Testing for Low Battery
Power-ON Reset
Internal Reverse Battery Protection
ABSOLUTE MAXIMUM RATINGS
(Voltages are referenced to V
SS
)
Supply Voltage Range,
V
DD
................................
-0.5 V to +15 V
Reverse Battery (10.5 V) .......................
20 s
Input Voltage Range,
V
IN
........................
-0.3 V to V
DD
+ 0.3 V
Input Current, I
IN
...............................
10 mA
Operating Temperature Range,
T
A
.....................................
0
°
C to +50
°
C
Storage Temperature Range,
T
S
...............................
-55
°
C to +125
°
C
CAUTION: CMOS devices have input static
protection but are susceptible to damage when
exposed to extremely high static electrical
charges.
Always order by complete part number:
A5355CA
.
5355
SMOKE DETECTOR
with INTERCONNECT
CIRCUIT DESCRIPTION
The A5355CA is a low-current CMOS circuit providing
all of the required features for an ionization-type smoke
detector.
Oscillator.
An internal oscillator operates with a period of
1.67 seconds during no-smoke conditions. Every 1.67
seconds, internal power is applied to the entire circuit and
a check is made for smoke. Every 24 clock cycles (40
seconds), the LED is pulsed and a check is made for low
battery by comparing V
DD
to an internal reference.
Since very-low currents are used in the device, the
oscillator capacitor at pin 12 should be a low-leakage type
(PTFE, polystyrene, or polypropylene).
Detector Circuitry.
An active guard is provided on both
pins adjacent to the detector input (pin 15). The voltage
at pins 14 and 16 will be within 100 mV of the input. This
will keep surface leakage currents to a minimum and
provide a method of measuring the input voltage without
loading the ionization chamber. The active guard ampli-
fier is not power strobed and thus provides constant
protection from surface leakage currents. The detector
input has internal diode protection against static damage.
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 must be
externally adjusted to the individual characteristics of the
ionization chamber by connecting resistors between pin
13 and V
DD
, and 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 decreased
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.
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
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.
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