A5303_16 Datasheet, PDF (1/15 Pages) Allegro MicroSystems – Photoelectric Smoke Detector with Interconnect, Timer, and Latching Alarm Indicator

A5303
Photoelectric Smoke Detector
with Interconnect, Timer, and Latching Alarm Indicator
Features and Benefits
▪ Low average standby current allows 10-year battery life
▪ 2.3 to 5.5 V operating range
▪ Interconnect option
▪ Logic outputs to control an external sound IC
▪ Low battery detection and warning
▪ Chamber sensitivity test and warning
▪ Triple horn-chirp to distinguish chamber warning
▪ Power-on reset (POR)
▪ Digital filter on I/O provides significant noise immunity
▪ Timer (hush) mode for enabling reduced sensitivity period
▪ Built-in circuits to reduce false triggering
▪ ESD protection circuitry on all pins
▪ Temporal Horn Pattern, per UL217, NFPA72, ISO8201
▪ Latching alarm indicator identifies alarm-initiating devices
Packages:
20-pin TSSOP
(LE package)
Not to scale
Description
The A5303 is a low-current BiCMOS photoelectric smoke
detector circuit with ultra-low standby current and can operate
for 10 years powered by inexpensive batteries. This device can
be used with an infrared optical chamber to sense light scattered
from smoke particles. A networking capability allows 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.
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 45% to provide
hysteresis. High gain is used during pushbutton test and to
periodically monitor the chamber sensitivity during standby.
The internal oscillator and timing circuitry minimize standby
power by sensing for smoke for only 100 μs once 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 to occur.
20-contact QFN
4 mm × 4 mm × 0.75 mm
(ES package)
TheA5303 is supplied in a thin profile (<1.2 mm overall height)
20-pin TSSOP (LE) package (0.65 mm nominal lead pitch)
and a 20-contact QFN (ES) package with exposed thermal
pad. Both packages are lead (Pb) free with 100% matte tin
leadframe plating.
Typical Application Diagram
V_DD
R1 ^{3 kΩ}
5 kΩ
R2
56 nF
C1
5.6 nF 560 Ω
C2
200 kΩ
DETECT
1 kΩ
V_DD
100 µF
Smoke
Chamber
3Ω
STROBE
IRED
ISET
Connect HUSH to
VSS to disable
timer mode
HUSH
VSS
To / from
other units
220 Ω
Gain
Select
V_DD -
1.6 V
V_DD
1.2 V
Low Batt
Control
Logic
VDD
LVSET
Low Batt
Sample
TEST
BLINK
SOUT0
SOUT1
SOUT2
HORN
LED
V_DD 3 V
10 µF
A
Push-to-test
B
Voice IC outputs
Output to optional
boost converter to
drive a piezo horn
Red LED
A
A resistor connected
between this pin and
VDD or VSS adjusts
the low-battery threshold
B In standby, BLINK = VDD
causes LED to blink,
BLINK = V _SS causes
LED not to blink
OSC
Timing
OSCCAP
TRES
100 kΩ
1500 pf
10 ΜΩ
5303-DS, Rev. 1