A5358CAT Datasheet, PDF (1/13 Pages) Allegro MicroSystems – Photoelectric Smoke Detector with Interconnect and Timer

A5358
Photoelectric Smoke Detector
with Interconnect and Timer
Features and Benefits
▪ Low average standby current for long battery life
▪ Interconnect up to 50 detectors
▪ Piezoelectric horn driver
▪ Low battery detection (all internal)
▪ Chamber sensitivity test and alarm
▪ Power-on reset (POR)
▪ Internal timer and control for reduced sensitivity mode
▪ Built-in circuits to reduce false triggering
▪ 6 to 12 V operating range
▪ ESD protection circuitry on all pins
Packages:
16-pin DIP
(Package A)
16-pin SOICW
(Package LW)
Not to scale
Description
The A5358 is a low-current BiCMOS circuit providing all of
the required features for a photoelectric type smoke detector.
This device can be used with an infrared photoelectric chamber
to sense scattered light from smoke particles. A networking
capability allows as many as 50 units to be interconnected so
that if any unit senses smoke all units will sound an alarm.
Special features are incorporated in the design to facilitate
calibration and testing of the finished detector. The device is
designed for applications that comply with European Standard
EN 14604 and British Standard BS 5446, Part 1.
A variable-gain photoamplifier can be directly interfaced to
an infrared emitter-detector pair. The amplifier gain levels are
determined by two external capacitors and are internally selected
depending on the operating mode. Low gain is selected during
standby and timer modes. During a local alarm, this low gain
is increased (internally) by approximately 10% to reduce false
triggering. High gain is used during pushbutton test and to
periodically monitor the chamber sensitivity during standby.
The internal oscillator and timing circuitry keep standby power
to a minimum by sensing for smoke for only 100 μs every 10 s.
A special three-stage–speedup sensing scheme is incorporated
to minimize the time to an audible alarm and also to reduce
false triggering. Chamber sensitivity is periodically monitored
and two consecutive cycles of degraded sensitivity are required
for a warning signal (chirp) to occur.
The A5358 is supplied in a 16-pin dual in-line plastic package
(suffix A), and for surface mount, a 16-pin SOICW (suffix
LW). The lead (Pb) free versions (suffix –T) have 100% matte-
tin leadframe plating. The devices are rated for continuous
operation over the temperature range of –25°C to 75°C.
Typical Application Diagram
Rx1
A
Rx2
26110.10-DS, Rev. I
V_DD
8.2 kΩ
5 kΩ
4.7 kΩ
0.047 μF
560 Ω
4700 pF
200 kΩ
1 kΩ
Smoke
Chamber
100 μF
22 Ω
To / from
other units
220 Ω
1 _C1
2 _C2
3 _DETECT
4 _STROBE
5 _VDD
6 _IRED
7 _I/O
8
HORN1
9V
A5358
TEST ¹⁶
22 μF
Push-to-Test
HUSH ¹⁵
B
VSS ¹⁴
Red LED
1500 pF
13
TIMING RES
100 kΩ
10 MΩ
OSC CAP ¹²
330 Ω
LED ¹¹
FEEDBACK ¹⁰
HORN2 ⁹
220 kΩ C
1000 pF
C
Piezo Horn
1.5 MΩ C
A ^{Connect to allow timer mode}
("hush") operation
B ^{Connect HUSH to VSS}
to disable timer mode
C ^{Value of component can vary,}
based on the piezoelectric horn used