A5358A low-current BiCMOS circuit that provides all the features needed for a photoelectric smoke detector. The device can be used with an infrared photoelectric chamber to sense light emitted by smoke particles. Networking allows up to 50 devices to be interconnected, all with audible alarms when smoke is detected by any device. Special features are also integrated into 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.
The variable gain optical amplifier allows direct interaction with the IR emitter-detector pair. The amplifier gain level is determined by two external capacitors and selected internally based on the operating mode. Select low gain in standby and timer modes. When a local alarm occurs, the low gain increases (internally) by about 10% to reduce false triggering. High gain is used when periodically monitoring optical chamber sensitivity in key test or standby mode.
The built-in oscillator and timing circuitry sense smoke for only 100 milliseconds every 10 seconds, significantly reducing standby power consumption. In addition, a special third-order acceleration sensing scheme is integrated to reduce the time to sound an audible alarm while reducing false triggering. The sensitivity of the optical chamber is monitored periodically, and an alarm signal (chirp) is issued when two consecutive periods of sensitivity decline occur.
- Low average standby current for longer battery life
- Interconnect more than 50 detectors
- Piezoelectric alarm driver
- Low battery detection (both internal)
- Light chamber sensitivity test and alarm
- Power-On Reset (POR)
- Internal timer and control in low sensitivity mode
- Built-in circuitry to reduce false triggering
- 6 to 12 volt operating range
- All pins have ESD protection circuitry