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PDF A5348 Data sheet ( Hoja de datos )
| Número de pieza | A5348 | |
| Descripción | Ionization Smoke Detector | |
| Fabricantes | Allegro | |
| Logotipo |  |
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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
Package: 16-pin DIP (suffix A):
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.
Not to scale
Typical Application
50 kΩ
To / from
other units
9V
Timer
Mode
1
200 Ω 2
C3
4
330 Ω 5
200 kΩ
TIMER START
GUARD2
I/O DETECT IN
A5348
LOW-V SET
GUARD1
TIMER OUT
SENSITIVITY SET
LED OSC CAP
16
15
14
13
12
8.2 MΩ
6 VDD
7 TIMING RES
11
HORN2
10
HORN1
1 μF 8 FEEDBACK
9
VSS
B
200 k Ω
Push
to Test
A
0.1 μF
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.
1.5 MΩ
D
220 kΩ
D
0.001 μF
D
26110.3 Rev. 4
1 page  
A5348
Ionization Smoke Detector
with Interconnect and Timer
ELECTRICAL CHARACTERISTICS1,2 (continued) at TA = 25°C, VDD = 9.0 V, VSS = 0 V, COSCCAP = 0.1 μF,
RTIMINGRES = 8.2 MΩ (unless otherwise noted)
Characteristic
Symbol
Test Conditions
Test Pin
Min.
Typ.
Max.
Units
I/O Current
IIOL No alarm, VI/O = VDD – 2.0 V
IIOH Local alarm, VI/O = VDD – 2.0 V
2
2
25 —
–7.5 —
60
—
I/O Alarm Voltage
VIH(IO) External “alarm” in
2 3.0 — —
I/O Delay
tr(io) Local or test alarm to I/O active
2
— 3.0 —
1Negative current is defined as coming out of the specified device pin (sourcing).
2Alarm (smoke) condition is defined as VDETECTIN < VSENSITIVITYSET; no alarm (no smoke) condition is defined as VDETECTIN > VSENSITIVITYSET.
μA
mA
V
s
Circuit Description
The A5348 is a low-current, BiCMOS circuit providing all of the currents. The detector input has internal diode protection against
required features for an ionization-type smoke detector.
electrostatic damage.
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 VDD 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 VSENSITIVITYSET 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. VGUARD1
and VGUARD2 will be within 100 mV of VDETECTIN. 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
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:
VSENSITIVITYSET = VDD / 2 .
To increase sensitivity, a resistor can be connected between
SENSITIVITY SET and VDD, with the value:
where
RSENSITIVITYSET = 1.1E6 × K / (1 – K) ,
K = VDD / VSENSITIVITYSET – 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
5 Page | ||
| Páginas | Total 9 Páginas | |
| PDF Descargar | [ Datasheet A5348.PDF ] | |
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