MC145012

The CMOS MC145012 is an advanced smoke detector component containing sophisticated verylowpower analog and digital circuitry. The IC is used with an infrared photoelectric chamber. Detection is accomplished by sensing scattered light from minute smoke particles or other aerosols. When detection occurs, a pulsating alarm is sounded via onchip pushpull drivers and an external piezoelectric transducer.

The variablegain photo amplifier allows direct interface to IR detectors (photodiodes). Two external capacitors, C1 and C2, C1 being the larger, determine the gain settings. Low gain is selected by the IC during most of the standby state. Medium gain is selected during a localsmoke condition. High gain is used during pushbutton test. During standby, the special monitor circuit which periodically checks for degraded chamber sensitivity uses high gain also.

The I/O pin, in combination with V_SS, can be used to interconnect up to 40 units for common signaling. An onchip current sink provides noise immunity when the I/O is an input. A localsmoke condition activates the shortcircuit
protected I/O driver, thereby signaling remote smoke to the interconnected units. Additionally, the I/O pin can be used to activate escape lights, enable auxiliary or remote alarms, and/or initiate autodialers.

While in standby, the lowsupply detection circuitry conducts periodic checks using a pulsed load current from the LED pin. The trip point is set using two external resistors. The supply for the MC145012 can be a 9 V battery.

A visible LED flash accompanying a pulsating audible alarm indicates a localsmoke condition. A pulsating audible alarm with no LED flash indicates a remotesmoke condition. A beep or chirp occurring virtually simultaneously with an LED flash indicates a lowsupply condition. A beep or chirp occurring halfway between LED flashes indicates degraded chamber sensitivity. A lowsupply condition does not affect the smoke detection capability if _VDD 6 V. Therefore, the lowsupply condition and degraded chamber sensitivity can be further distinguished by performing a pushbutton (chamber) test.