A5303
Photoelectric Smoke Detector
with Interconnect, Timer, and Latching Alarm Indicator
Features and Benefits
Description
▪ Low average standby current allows 10-year battery life
▪ 2.3 to 5.5 V operating range
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
beusedwithaninfraredopticalchambertosenselightscattered
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.
▪ 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
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
selecteddependingontheoperatingmode.Lowgainisselected
duringstandbyandtimermodes. Duringalocalalarm, thislow
gainisincreased(internally)byapproximately45%toprovide
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.
Aspecial three-stage-speedup sensing scheme is incorporated
to minimize the time to an audible alarm and also to reduce
falsetriggering. Chambersensitivityisperiodicallymonitored
andtwoconsecutivecyclesofdegradedsensitivityarerequired
for a warning signal to occur.
Package: 20-pin TSSOP (suffix LE)
The A5303 is supplied in a thin profile (<1.2 mm overall
height) 20-pin TSSOPpackage (0.65 mm nominal lead pitch).
The package is lead (Pb) free with 100% matte tin leadframe
plating.
Not to scale
Typical Application Diagram
To / from
other units
220 Ω
VDD
3 V
VDD
VDD
1.2 V
56 nF
VDD
C1
C2
10 μF
Gain
LVSET
A
B
3 kΩ
5 k Ω
5.6 nF
560 Ω
R1
R2
Select
Low Batt
Low Batt
Sample
Push-to-test
200 kΩ
TEST
A resistor connected
between this pin and
VDD or VSS adjusts
the low-battery threshold
DETECT
STROBE
BLINK
A
B
SOUT0
SOUT1
SOUT2
Smoke
Chamber
Control
Logic
VDD
1.6 V
-
Voice IC outputs
In standby, BLINK = VDD
causes LED to blink,
causes
BLINK = VSS
LED not to blink
1 kΩ
Output to optional
boost converter to
drive a piezo horn
VDD
IRED
ISET
HORN
LED
100 μF
3 Ω
Red LED
HUSH
VSS
OSCCAP
TRES
OSC
Timing
Connect HUSH to
VSS to disable
timer mode
1500 pf
100 kΩ
10 ΜΩ
5303-DS