A5303, A5358 and A5366: Photoelectric Smoke Detectors

A and LW Package Image


Top Features

Smoke detector IC’s designed for photoelectric chambers provide all the functions necessary to sense and respond to smoke in the air when combined with a smoke detection chamber. Used in both residential and commercial infrastructure Allegro’s smoke detection IC’s provide a wide variety of features including 10year battery life, alarm networking, and temporal as well as repetitive alarm modes. 

The A5303 is a low-current photoelectric smoke detector circuit with ultra-low standby current and can operate for 10 years powered by inexpensive batteries. The A5366 and A5358 are a low-current sensing IC’s that provide all of the required features for a photoelectric type smoke detector. These devices can be used with an infrared photoelectric chamber to sense scattered light from smoke particles. 

A variable-gain photoamplifier can be directly interfaced to an infrared emitter-detector pair. 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.

Special features are incorporated in these designs to facilitate networking of detectors and calibration and testing of the finished detector. The device is recognized by Underwriters Laboratories for use in smoke alarms that comply with Standard UL217, or UL268, per file #S2113.

The A5303 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.

The A5366 and A5358 are 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.

  • Low average standby current (10-year battery life A5303)
  • 2.3 to 5.5 V operating range (A5303)
  • Interconnect option
  • Logic outputs to control an external horn driver (A5303)
  • Integrated piezo horn driver (A5366, A5358)
  • 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
  • Latching alarm indicator identifies alarm-initiating devices


A5303 Packaging: 

20-contact QFN (ES) package with exposed thermal pad, 20-pin TSSOP (LE) package


  Allegro 20-Pin 4mmx4mm QFN ES with wettable flank packageProduct Image

ES Package Documentation

LE Package Documentation

A5366 & A5358 Packaging:

16-pin dual in-line plastic package (suffix A), 16-pin SOICW (suffix LW)

A and LW Package Image

A Package Documentation

LW Package Documentation