The A5338CA from Allegro MicroSystems Europe is a low-current CMOS integrated circuit incorporating all of the required features for an ionisation-type smoke detector. The device is designed to comply with Underwriters Laboratories Specification UL217. The device features a networking capability that allows up to 125 units to be interconnected so that, if any unit senses smoke, all units will sound an alarm. In addition, special features are incorporated to facilitate alignment and test of the finished smoke detector.
The internal oscillator and timing circuitry keeps standby power to a minimum by powering down the device for 1.66 sec and sensing smoke for only 10 ms. Every 24 on/off cycles, a pulse check is made for low battery condition. By substituting other types of sensors or a switch for the ionisation detector, the low power device can be used in numerous other battery-operated safety/security applications.
Other features include a piezoelectric horn driver, guard outputs for detector input, power-on reset, internal reverse battery protection, and built-in hysteresis to reduce false triggering.
The A5338CA is supplied in a low-cost, 16-pin dual-inline plastic package. It is rated for continuous operation over the temperature range from 0°C to +50°C.