A5358CA

The A5358CA is a low-current BiCMOS circuit providing all of the required features for a photoelectric type smoke detector. This device can be used in conjunction with an infrared photoelectric chamber to sense scattered light from smoke particles. Special features are incorporated in the design to facilitate calibration and testing of the finished detector. The device is designed to comply with Underwriters Laboratories Specification UL217 and British Standard BS 5446, Part 1.

A variable-gain photo amplifier can be directly interfaced to an infrared emitter/detector pair. The amplifier gain levels are determined by two external capacitors that are then 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 ~10% to reduce false triggering. High gain is used during the pushbutton test and during standby to periodically monitor the chamber sensitivity.

The internal oscillator and timing circuitry keeps standby power to a minimum by sensing for smoke every 10 seconds in a 10 s window. A special three-stage speedup sensing scheme is incorporated to minimize the time to an audible alarm and also to reduce false triggering. Also, two consecutive cycles of degraded chamber sensitivity are required for a warning signal to occur.

The A5358CA is supplied in a low-cost 16-pin dual in-line plastic package. It is rated for continuous operation over the temperature range of -25°C to +75°C. The Pb (lead) free version has 100% matte tin leadframe plating.