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.