A5358

• Low average standby current for long battery life
• Interconnect up to 50 detectors
• Piezoelectric horn driver
• Low battery detection (all internal)
• Chamber sensitivity test and alarm
• Power-on reset (POR)
• Internal timer and control for reduced sensitivity mode
• Built-in circuits to reduce false triggering
• 6 to 12 V operating range
• ESD protection circuitry on all pins

Description

The A5358 is a low-current BiCMOS circuit providing all of the required features for a photoelectric type smoke detector. This device can be used with an infrared photoelectric chamber to sense scattered light from smoke particles. A networking capability allows as many as 50 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. The device is designed for applications that comply with European Standard EN 14604 and British Standard BS 5446, Part 1.

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 10% to reduce false triggering. High gain is used during pushbutton test and to periodically monitor the chamber sensitivity during standby.

The internal oscillator and timing circuitry keep standby power to a minimum by sensing for smoke for only 100 µs every 10 s. A special three-stagepeedup 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 (chirp) to occur.

The A5358 is 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 ) have 100% mattetin leadframe plating. The devices are rated for continuous operation over the temperature range of ?5°C to 75°C.