
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
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.
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
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
andtwoconsecutivecyclesofdegradedsensitivityarerequired
for a warning signal to occur.
TheA5303issuppliedinathinprofile(<1.2mmoverallheight)
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.
5303-DS, Rev. 1
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
Photoelectric Smoke Detector
with Interconnect, Timer, and Latching Alarm Indicator
Packages:
Not to scale
A5303
Typical Application Diagram
Control
Logic
SOUT0
VDD
TEST
C1
56 nF
C2
5.6 nF
DETECT
Gain
Select
STROBE
IRED
VDD
OSC
Timing
Low Batt
1.2 V
3 V
100 F
LED
VSS
560
200 k
10 F
VDD -
1.6 V
OSCCAP
1500 pf
Push-to-test
HUSH
Connect HUSH to
VSS to disable
timer mode
C
on
ne
ct
to
al
lo
w
tim
er
(h
us
h)
m
od
e
op
er
at
io
n
ISET
LVSET
Low Batt
Sample
A
A A resistor connected
between this pin and
VDD or VSS adjusts
the low-battery threshold
SOUT1
Voice IC outputs
10 Μ
100 k
SOUT2
TRES
I/O
220
To / from
other units
VDD
BLINK
In standby, BLINK = VDD
causes LED to blink,
BLINK = VSS causes
LED not to blink
HORN
Output to optional
boost converter to
drive a piezo horn
Smoke
Chamber
Red LED
B
R1
R2
5 k
3 k
3
1 k
20-contact QFN
4 mm × 4 mm × 0.75 mm
(ES package)
20-pin TSSOP
(LE package)