A5348
Ionization Smoke Detector
with Interconnect and Timer
Features and Benefits
▪
Low average standby current for long battery life
▪
Interconnect up to 125 detectors
▪
Piezoelectric horn driver
▪
Guard outputs for detector input
▪
Pulse testing for low battery
▪
Power-on reset (POR)
▪
Internal reverse battery protection
▪
Timer (Hush) mode for enabling reduced sensitivity period
▪
Built-in hysteresis reduces false triggering
Description
The A5348 is a low-current, BiCMOS 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 their alarm. In addition, special features are
incorporated to facilitate alignment and test of the finished
smoke detector.
The internal oscillator and timing circuitry keep standby power
to a minimum by powering down the device for 1.66 seconds
and sensing for smoke for only 10 ms. Every 24 on-off cycles,
a check is made for a 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 A5348 is supplied in a low-cost 16-pin dual in-line plastic
package (DIP). It is rated for continuous operation over the
temperature range of –10°C to 60°C. The Pb (lead) free version
(suffix –T) has 100% matte tin leadframe plating.
Package: 16-pin DIP (suffix A):
Not to scale
Typical Application
Timer
Mode
200 kΩ
1
TIMER START
I/O
GUARD2
DETECT IN
16
15
14
200 k
Ω
Push
to Test
A
Use an external resistor to adjust
sensitivity for a particular smoke chamber.
B
Select resistor to reduce sensitivity
during Timer mode.
C
A resistor to VSS or VDD may
be added to this pin to modify
low battery voltage threshold.
D
Value of component will vary, based on
the piezoelectric horn used.
50 kΩ
To / from
other units
200
Ω
2
3
4
A5348
LOW-V SET
TIMER OUT
SENSITIVITY SET
LED
VDD
TIMING RES
FEEDBACK
B
C
GUARD1
13
12
330
Ω
9V
A
5
6
OSC CAP
HORN2
HORN1
VSS
0.1
μF
11
10
9
1.5 MΩ
D
220 kΩ
D
8.2 MΩ
1
μF
7
8
0.001
μF
D
26110.3 Rev. 4
A5348
Selection Guide
Part Number
A5348CA-T
A5348CA
Pb-Free
Yes
–
Packing
Ionization Smoke Detector
with Interconnect and Timer
25 pieces per tube
Absolute Maximum Ratings*
Characteristic
Symbol
Notes
Rating
Units
Supply Voltage Range
Input Voltage Range
Reverse Battery Condition Duration
Input Current
Operating Ambient Temperature
Junction Temperature
Storage Temperature Range
V
DD
V
IN
t
RBAT
I
IN
T
A
T
J
(max)
T
stg
Referenced to V
SS
Referenced to V
SS
10.5 V
–0.5 to 15
–0.3 to V
DD
+ 0.3
20
10
–10 to 60
150
–55 to 125
V
V
s
mA
ºC
ºC
ºC
* CAUTION:BiCMOS devices have input static protection but are susceptible to damage when exposed to extremely high static electrical charges.
THERMAL CHARACTERISTICS
Characteristic
Package Thermal Resistance
Symbol
R
θJA
Test Conditions*
4-layer PCB based on JEDEC standard
Value Units
38
ºC/W
*Additional thermal information available on Allegro website.
Terminal List Table
Number
1
2
Name
TIMER START
I/O
LOW-V SET
TIMER OUT
LED
VDD
TIMING RES
FEEDBACK
VSS
HORN1
HORN2
OSC CAP
SENSITIVITY SET
GUARD1
DETECT IN
GUARD2
Function
Input to start reduced sensitivity timer mode
Input/output to interconnected detectors
Optionally used with a resistor to adjust low-battery
threshold
Optionally used with a resistor to adjust sensitivity
during timer mode
Output to drive visible LED
Positive supply voltage
Terminal for timing resistor, sets internal bias
(affects timing)
Input for driving piezoelectric horn
Negative supply voltage
Output for driving piezoelectric horn
Complementary output for driving piezoelectric horn
Terminal for charging/discharging an external
capacitor to run the oscillator
Optionally used with a resistor to adjust sensitivity
for a specific chamber
Active guard 1 for detector input
Input from detector chamber
Active guard 2 for detector input
Pin-out Diagram
3
4
TIMER START 1
I/O 2
LOW-V SET 3
TIMER OUT 4
LED 5
VDD 6
TIMING RES 7
FEEDBACK 8
16 GUARD2
15 DETECT IN
14 GUARD1
13 SENSITIVITY SET
12 OSC CAP
11 HORN2
10 HORN1
9 VSS
5
6
7
8
9
10
11
12
13
14
15
16
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A5348
Ionization Smoke Detector
with Interconnect and Timer
Functional Block Diagram
I/O
+Supply
9V
VDD
Band
Gap
V
DD
FEEDBACK
LBSamp
HORN2
HORN1
Low Battery
Sample
600 kΩ
_
Low Battery
Comparator
Logic
LED
+ V
DD
LOW-V SET
+
500 kΩ
+
_
Smoke
Comparator
Smoke
Sample
1.1 MΩ
LBSamp
SSamp
Oscillator
and Timing
OSC CAP
TIMER OUT
Power-on
Reset
TIMING RES
SENSITIVITY SET
SSamp
+ V
DD
-Supply
VSS
+
_
GUARD1
DETECT IN
GUARD2
TIMER START
+ V
DD
ION CHAMBER
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A5348
Ionization Smoke Detector
with Interconnect and Timer
ELECTRICAL CHARACTERISTICS
1,2
at T
A
= 25°C, V
DD
= 9.0 V, V
SS
= 0 V, C
OSCCAP
= 0.1
μF,
R
TIMINGRES
= 8.2 MΩ (unless otherwise noted)
Characteristic
Supply Voltage Range
Supply Current
Detector Input Current
Input Offset Voltage
Hysteresis
Common Mode Range
Active Guard Impedance
Oscillator Period
Oscillator Pulse Width
Timer Mode Duration
Low-Battery Threshold
Sensitivity Adjust Voltage
Symbol
V
DD
I
DD
I
DETECTIN
V
OS(GUARD1)
V
OS(GUARD2)
V
OS
V
HYS
V
CM(guard)
V
CM
Z
AG1
Z
AG2
t
osc
t
osc(alarm)
t
w(osc)
t
timer
V
DD(th)
V
SET
V
OL
Horn Output Voltage
V
OH
Horn Output On-Time
Horn Output Off-Time
TIMER START Logic Levels
TIMER START Input Current
TIMER OUT Pulldown Current
LED Output-On Current
LED Output On-Time
t
on(horn)
t
w(horn)
t
off(horn)
t
horn
V
IH
V
IL
I
IN
I
PD
I
LED
t
w(LED)
t
LED1
t
LED2
t
LED3
t
LED4
Test Conditions
Operating
V
DD
= 9.0 V, no alarm, no loads
V
DD
= 12 V, no alarm, no loads
0% to 40% RH, V
IN
= 0 to 9.0 V
Active GUARD1
Active GUARD2
Detect comparator
No alarm to alarm
Guard amplifier
Smoke comparator
GUARD1 to VSS
GUARD2 to VSS
No alarm
Local or remote alarm
After TIMER START high-to-low,
no smoke
T
A
= 0°C to 50°C,
LOW-V SET open circuit
V
SENSITIVITYSET
/ V
DD
,
SENSITIVITY SET 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
Local or remote alarm
Low battery
Local or remote alarm
Low battery
Test Pin
6
6
6
15
14, 15
16, 15
15, 13
13
14, 15
13, 15
14
16
12
12
12
4
6
13
10, 11
10, 11
10, 11
10, 11
10,11
10, 11
10, 11
10, 11
1
1
1
4
5
5
5
5
5
5
Min.
6.0
—
—
—
—
—
—
90
2.0
0.5
—
—
1.34
37.50
8.0
8.0
7.2
48.5
—
—
8.5
6.3
120
8
60
32
3.5
—
20
500
10
8.0
32
8.0
0.76
—
Typ.
9.0
5.0
—
—
—
—
—
130
—
—
10
500
1.67
41.67
10
10
—
50
0.1
—
8.8
—
160
10
80
40
—
—
—
—
—
10
40
10
0.97
No LED
pulses
Max.
12
9.0
12
±1.0
±100
±100
±50
170
V
DD
– 0.5
V
DD
– 2.0
—
—
2.00
45.84
12
12
7.8
51.5
0.5
0.9
—
—
208
12
104
48
—
1.5
80
—
—
12
48
12
1.14
—
Units
V
μA
μA
pA
mV
mV
mV
mV
V
V
kΩ
kΩ
s
ms
ms
min
V
%V
DD
V
V
V
V
ms
ms
ms
s
V
V
μA
μA
mA
ms
s
s
s
s
V
TIMERSTART
= 9.0 V
V
TIMEROUT
= 0.5 V
V
DD
= 7.2 V, V
LED
= 1.0 V
No alarm, in standby
No alarm, timer mode
Local alarm or test alarm
Remote alarm, no local smoke
LED Output Off-Time
Continued on the next page…
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
A5348
Ionization Smoke Detector
with Interconnect and Timer
ELECTRICAL CHARACTERISTICS
1,2
(continued) at T
A
= 25°C, V
DD
= 9.0 V, V
SS
= 0 V, C
OSCCAP
= 0.1
μF,
R
TIMINGRES
= 8.2 MΩ (unless otherwise noted)
Symbol
Test Conditions
Test Pin
Min.
Typ.
Max.
Units
No alarm, V
I/O
= V
DD
– 2.0 V
2
25
—
60
μA
I
IOL
I/O Current
Local alarm, V
I/O
= V
DD
– 2.0 V
2
–7.5
—
—
mA
I
IOH
I/O Alarm Voltage
V
IH(IO)
External “alarm” in
2
3.0
—
—
V
I/O Delay
t
r(io)
Local or test alarm to I/O active
2
—
3.0
—
s
1
Negative current is defined as coming out of the specified device pin (sourcing).
2
Alarm (smoke) condition is defined as V
DETECTIN
< V
SENSITIVITYSET
; no alarm (no smoke) condition is defined as V
DETECTIN
> V
SENSITIVITYSET
.
Characteristic
Circuit Description
The A5348 is a low-current, BiCMOS 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 for 10 ms and a check is made for
smoke. Every 24 clock cycles (approximately 40 seconds), the
LED pin is pulsed and a check is made for low battery by com-
paring V
DD
to an internal reference. Because very-low currents
are used in the device, the oscillator capacitor at the OSC CAP
pin should be a low-leakage type (PTFE, polystyrene, or polypro-
pylene).
Detector Circuitry
When the voltage on the DETECT IN pin is less than the volt-
age on the SENSITIVITY SET pin, the A5348 evaluates this as a
smoke condition.
During a smoke condition, the resistor divider
network that sets the sensitivity (also referred to as the
smoke trip
point)
is altered to increase V
SENSITIVITYSET
by 130 mV typical
(with no external connections on the SENSITIVITY SET pin).
This provides hysteresis and reduces false triggering.
An active guard is provided on GUARD1 and GUARD2, the two
pins adjacent to the detector input, the DETECT IN pin. V
GUARD1
and V
GUARD2
will be within 100 mV of V
DETECTIN
. This will
keep surface leakage currents to a minimum and provide a
method of measuring the input voltage without loading the ion-
ization 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
electrostatic 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 checked and further
alarm output will be inhibited if smoke is not sensed. During a
smoke condition, the low-battery alarm is inhibited and the LED
is pulsed approximately once every second.
Sensitivity Adjust
The detector sensitivity to smoke is set internally by a voltage
divider connected between VDD and VSS. The sensitivity can,
however, be externally adjusted to the individual characteristics
of the ionization chamber by connecting a resistor between the
SENSITIVITY SET pin and either the VDD or VSS pins.
With no external connections on the SENSITIVITY SET pin,
while the A5348 is checking for smoke:
V
SENSITIVITYSET
= V
DD
/ 2 .
To increase sensitivity, a resistor can be connected between
SENSITIVITY SET and VDD, with the value:
R
SENSITIVITYSET
= 1.1E6 ×
K
/ (1 –
K)
,
where
K
=
V
DD
/
V
SENSITIVITYSET
– 1 .
To decrease sensitivity, a resistor can be connected between
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
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