MC145011

The CMOS MC145011 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 MC145011 is sounded via onchip pushpull drivers and an external piezoelectric transducer.

The variablegain photo amplifier MC145011 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 VSS, MC145011 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 shortcircuitprotected I/O driver, thereby signaling remote smoke to the interconnected units. Additionally, the I/O pin of MC145011 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 load current from the LED pin. The trip point is set using two externalresistors. The supply for the MC145011 must be a dc power source capable of supplying 35 mA continuously and 45 mA peak. When the MC145011 is in standby, an external LED is continuously illuminated to indicate that the device is receiving power.

An extinguished LED accompanied by a pulsating audible alarm indicates a localsmoke condition. A pulsating audible alarm with the LED illuminated indicates a remotesmoke condition. A beep or chirp indicates a lowsupply condition or degraded chamber sensitivity. A lowsupply condition does not affect the smoke detection capability if VDD6 V. Therefore, the lowsupply condition and degraded chamber sensitivity can be distinguished by performing a pushbutton (chamber) test. This circuit of MC145011 is designed to operate in smoke detector systems that comply with UL217 and UL268 specifications.