The MC145018, when used with an ionization chamber and a small number of external components, will detect smoke. When smoke is sensed, an alarm is sounded via an external piezoelectric transducer and internal drivers. This circuit is designed to operate in smoke detector systems that comply with UL217 and UL268 specifications.

• Ionization Type with On–Chip FET Input Comparator
• Piezoelectric Horn Driver
• Guard Outputs on Both Sides of Detect Input
• Input–Protection Diodes on the Detect Input
• Low–Battery Trip Point, Internally Set, can be Altered Via External Resistor
• Detect Threshold, Internally Set, can be Altered Via External Resistor
• Pulse Testing for Low Battery Uses LED for Battery Loading
• Comparator Output for Detect
• Internal Reverse Battery Protection
• Strobe Output for External Trim Resistors
• I/O Pin Allows Up to 40 Units to be Connected for Common Signaling
• Supports NFPA 72, ANSi 53.41, and ISO 8201 Audible Emergency Evacuation Signals
• Power–On Reset Places IC in Standby Mode