MOTOROLA MC145012DWR2

The CMOS MC145012 is an advanced smoke detector component incorporating sophisticated ultralow-power analog and digital circuitry. This IC is used in conjunction with an infrared photocell chamber. Detection is achieved by sensing scattered light from minute smoke particles or other aerosols. When smoke is detected, a pulsating alarm is sounded through an on-chip push-pull driver and an external piezoelectric transducer.

A variable-gain photoamplifier allows direct interfacing with an infrared detector (photodiode). Two external capacitors C1 and C2, with C1 being the larger, determine the gain setting. The IC selects low gain during most of the standby period. Medium gain is selected under local smoke conditions. High gain is used during pushbutton testing. A special monitoring circuit that periodically checks for chamber sensitivity degradation during standby also uses high gain.

The I/O pin, used in conjunction with VSS, allows up to 40 units to be interconnected for common signal transmission. On-chip current sinking provides noise suppression when I/O is an input. Local smoke conditions activate a short-circuit-protected I/O driver, thereby transmitting the remote smoke signal to interconnected units. In addition, the I/O pin can be used to activate escape lighting, enable auxiliary or remote alarms, and/or initiate an automatic dialer.

In the standby state, a low-supply detection circuit performs periodic checks using pulsed load current from the LED pin. Two external resistors are used to set the trip point. The MC145012 can be powered by a 9 V battery.

Visible LED flashing accompanying the pulsating audible alarm indicates a local smoke condition. A pulsating audible alarm without LED flashing indicates a remote smoke condition. A beep or chirp occurring nearly simultaneously with the LED flash indicates a low-supply condition. A beep or chirp occurring between LED flashes indicates chamber sensitivity degradation. If VDD ≥ 6 V, a low-supply condition does not affect smoke detection capability. Therefore, a low-supply condition and chamber sensitivity degradation can be further distinguished by performing a pushbutton (chamber) test.

• Smoke detection systems
• Battery-powered applications
• Emergency light activation
• Auxiliary alarms
• Remote alarms
• Auto dialers