5368
SMOKE DETECTOR
WITH INTERCONNECT AND TIMER
The A5368CA 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 A5368CA 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.
TIMER START
I/O
LOW-V SET
TIMER OUT
LED
+ SUPPLY
TIMING RES.
FEEDBACK
1
2
3
4
5
6
7
8
V
SS
V
DD
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
26110.8*
OSC. &
TIMING
HORN
DRIVER
Dwg. PC-004
FEATURES
s
s
s
s
s
s
s
s
s
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.
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
Internal Timer & Control for Reduced Sensitivity
Built-In Hysteresis Reduces False Triggering
Temporal Horn Pattern
Always order by complete part number:
A5368CA .
5368
SMOKE DETECTOR
WITH
INTERCONNECT
AND
TIMER
FUNCTIONAL BLOCK DIAGRAM AND TYPICAL APPLICATION
+ SUPPLY V
6
9V
DD
I/O
2
V DD
FEEDBACK
8
11
HORN
2
+
3
LOW-V
SET
–
+
LOGIC
10
HORN 1
5
LED
+V
SENSITIVITY
SET
– SUPPLY
9
V SS
14
GUARD 1
+V
DETECT. 15
IN
16
GUARD 2
1
TIMER
START
–
+
–
+
13
POWER-ON
RESET
TIMING RES.
7
OSCILLATOR
& TIMING
OSC. CAP.
12
4
TIMER OUT
+V
Dwg. FC-001B
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Copyright © 1998, Allegro MicroSystems, Inc.
5368
SMOKE DETECTOR
WITH
INTERCONNECT
AND
TIMER
ELECTRICAL CHARACTERISTICS at T
A
= +25
°
C, V
DD
= 9.0 V, V
SS
= 0 V, C
12
= 0.1
µ
F,
R
7
= 8.2 M
Ω
(unless otherwise noted).
Test
Characteristic
Supply Voltage Range
Detector Input Current
Input Offset Voltage
Pin
6
15
14-15
16-15
15-13
Hysteresis
Common Mode Range
13
14-15
13-15
Active Guard Impedance
14
16
Oscillator Period
12
Test Conditions
Operating
0 to 40% RH, V
IN
= 0 to 9.0 V
Active Guard
Active Guard
Detect Comparator
No Alarm to Alarm
Guard Amplifier
Smoke Comparator
to V
SS
to V
SS
No Alarm
Alarm
Oscillator Pulse Width
Timer Period
Low Voltage Threshold
Sensitivity Adj. Voltage
Horn Output Voltage
4
4
6
13
10-11
After Pin 1 High-to-Low, No Smoke
T
A
= 0 to 50°C
V
13
/V
DD
, pin 13 open circuit
I
OUT
= 16 mA, V
DD
= 9.0 V
I
OUT
= 16 mA, V
DD
= 7.2 V
I
OUT
= -16 mA, V
DD
= 9.0 V
I
OUT
= -16 mA, V
DD
= 7.2 V
Horn Output ON Time
10-11
Alarm (see figure, time “A”)
Low Battery
Horn Output OFF Time
10-11
Alarm (see figure, time “B”)
Alarm (see figure, time “C”)
Low Battery
Timer Start Logic Levels
1
V
IH
V
IL
Min.
6.0
—
—
—
—
90
2.0
0.5
—
—
1.34
32
8.0
8.0
7.2
48.5
—
—
8.5
6.3
450
8.0
450
1350
32
4.5
—
Limits
Typ.
9.0
—
—
—
—
130
—
—
10
500
1.67
40
10
10
—
50
0.1
—
8.8
—
500
10
500
1500
40
—
—
Max.
12
±1.0
±100
±100
±50
170
V
DD
- 0.5
V
DD
- 2.0
—
—
2.00
48
12
12
7.8
51.5
0.5
0.9
—
—
550
12
550
1650
48
—
2.5
Units
V
pA
mV
mV
mV
mV
V
V
kΩ
kΩ
s
ms
ms
min
V
%
V
V
V
V
ms
ms
ms
ms
s
V
V
NOTE 1:
NOTE 2:
Continued next page .
. .
Negative current is defined as coming out of (sourcing) the specified device pin.
Alarm (Smoke) Condition is defined as V
15
< V
13
; No Alarm (No Smoke) Condition as V
15
> V
13
.
5368
SMOKE DETECTOR
WITH
INTERCONNECT
AND
TIMER
ELECTRICAL CHARACTERISTICS continued
Test
Characteristic
Timer Start Input Current
Timer Out Output Current
LED Output ON Current
LED Output ON Time
LED Output OFF Time
Pin
1
4
5
5
5
Test Conditions
V
IN
= 9.0 V
V
OUT
= 0.5 V
V
DD
= 7.2 V, V
OUT
= 1.0 V
No Local Alarm; Not Latched
No Alarm, In Standby
No Alarm, Timer Mode
I/O Current
2
No Alarm, V
I/O
= V
DD
- 2.0 V
Alarm, V
I/O
= V
DD
- 2.0 V
Charge Dump, V
I/O
= 1.0 V
I/O Charge Dump Duration
I/O Alarm Voltage
I/O Delay
Supply Current
2
2
2
6
After Local Alarm or Test
External “Alarm” In
“Alarm” Out
V
DD
= 9.0 V, No Alarm, No Loads
V
DD
= 12 V, No Alarm, No Loads
Min.
20
500
10
8.0
32
8.0
25
-7.5
5.0
1.33
3.0
—
—
—
—
—
—
10
40
10
—
—
—
1.66
—
3.0
5.0
—
Limits
Typ.
Max.
80
—
—
12
48
12
60
—
—
1.99
—
—
9.0
12
Units
µA
µA
mA
ms
s
s
µA
mA
mA
s
V
s
µA
µA
NOTE 1:
NOTE 2:
Negative current is defined as coming out of (sourcing) the specified device pin.
Alarm (Smoke) Condition is defined as V
15
< V
13
; No Alarm (No Smoke) Condition as V
15
> V
13
.
CIRCUIT DESCRIPTION
The A5368CA 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, polysty-
rene, or polypropylene).
Detector Circuitry.
When smoke is detected, the resistor divider
network that sets the sensitivity (smoke trip point) is altered to increase
the sensitivity set voltage (pin 13) by typically 130 mV with no exter-
nal connections to pins 3 or 13. This provides hysteresis and reduces
false triggering. 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 amplifier 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 0.5 s
ON, 0.5 s OFF, 0.5 s ON, 0.5 s OFF, 0.5 s ON, 1.5 s OFF (temporal
horn pattern). During the OFF time, smoke is 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.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
5368
SMOKE DETECTOR
WITH
INTERCONNECT
AND
TIMER
Sensitivity Adjust.
The detector sensitiv-
ity 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
sensitivity (“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, how-
ever, 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
sound their associated horns after a nominal 3
second delay. The LED is suppressed when
an alarm is signaled from an interconnected
TYPICAL APPLICATION
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-005A
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.
unit. An internal NMOS device acts as a charge dump to aid in appli-
cations involving a large (distributed) capacitance on pin 2. The
charge dump is activated only on the removal of a local alarm.
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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