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.

The A5303 is supplied in a thin profile (<1.2 mm overall

height) 20-pin TSSOP package (0.65 mm nominal lead pitch).

The package is lead (Pb) free with 100% matte tin leadframe

plating.

5303-DS

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

Package: 20-pin TSSOP (suffix LE)

Not to scale

A5303

Typical Application Diagram

Control

Logic

SOUT0

VDD

TEST

C1

56 nF

C2

5.6 nF

DETECT

Gain

Select

STROBE

IRED

OSC

Timing

Low Batt

1.2 V

3 V

100 μF

LED

VSS

560 Ω

200 kΩ

10 μF

1.6 V

OSCCAP

1500 pf

Push-to-test

HUSH

Connect HUSH to

VSS to disable

timer mode

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 ΜΩ

100 kΩ

SOUT2

TRES

220 Ω

To / from

other units

BLINK

causes LED to blink,

BLINK = V

LED not to blink

HORN

Output to optional

boost converter to

drive a piezo horn

Smoke

Chamber

Red LED

B

B

R1

R2

5 k Ω

3 kΩ

3 Ω

1 k Ω