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MC146010

Low Power CMOS Photoelectric Smoke Detector IC

Freescale Semiconductor 

The load for the low-supply test is non-coincident with the

smoke tests, chamber sensitivity test, pushbutton test, or any

alarm signals.

The LED also provides a visual indication of the detector

status as follows, assuming the component values shown in

Figure 4:

Standby (includes low-supply and chamber sensitivity

tests) — Pulses every 32.4 seconds.

Local Smoke — Pulses every 2.0 seconds (typical)

Mute — Pulses every 2.0 seconds (typical)

Remote Smoke — No Pulses

Pushbutton test — Pulses every 2.0 seconds

OSC (PIN 12)

This pin is used in conjunction with external resistor R2

(7.5 MΩ) to VDD and external capacitor C3 (1500 pF) to VDD

to form an oscillator with a nominal period of 7.9 msec

(typical).

R1 (PIN 13)

This pin is use din conjunction with resistor R1(100 kΩ) to

pin 12 and C3 (1500 pF, see pin 12 description) to determine

the IRED pulse width. With this RC combination, the nominal

pulse width is 105 µs.

VSS (PIN 14)

This pin is the negative supply potential and the return for

the I/O pin. Pin 14 is usually tied to Ground.

LOW-SUPPLY TRIP (PIN 15)

This pin is connected to an external voltage which

determines the low-supply alarm threshold. The trip voltage

is obtained through a resistor divider connected between the

VDD and LED pins. The low-supply alarm threshold voltage

(in volts) = (5R7/R6)+5 where R6 and R7 are in the same

units.

TEST/MUTE (PIN 16)

This input has an on-chip pull-down device and is used to

manually invoke a test mode, a mute mode, or a calibration

mode.

The Pushbutton Test mode is initiated by a high level at

Pin 16 (usually a depression of a S.P.S.T. normally-open

pushbutton switch to VDD). After one oscillator cycle, the

IRED pulses approximately every 1.0 second, regardless of

the presence of smoke. Additionally, the amplifier gain is

increased by automatic selection of C1. Therefore the

background reflections in the smoke chamber may be

interpreted as smoke, generating a simulated smoke

condition. After the second IRED pulse, a successful test

activates the horn-driver and I/O circuits. The active I/O

allows remote signaling for a system testing. When the

Pushbutton Test switch is released, the Test input returns to

VSS due to the on-chip pull-down device. After one oscillator

cycle, the amplifier gain returns to normal, thereby removing

the simulated smoke condition. After two additional IRED

pulses, less than three seconds, the IC exits the alarm mode

and returns to standby timing.

The Pushbutton Test will also activate the Alarm Memory

feature. If there was a previous alarm detected by the unit,

the horn will chirp every ¼ second as long as the Test Button

is pressed. Upon releasing of the Test Button, Alarm memory

will be reset. Subsequent pressing of the Test Button will

result in a Pushbutton Test for simulated smoke.

Pressing the Test Button while in the MUTE mode will

result in resetting of MUTE (and additionally a normal

Pushbutton Test).

The MUTE mode (IMF) is initiated by a mid level voltage

(around ½ VDD) at pin 16. A parallel Mute Button to an

existing Test Button needs to be installed at the test pin. A

smoke condition must be present for the MUTE mode to be

activated. If a no smoke condition gets detected while in the

MUTE mode, the IMF 8 minute window gets reset. The unit

will return to Standby mode.

Once in the MUTE mode, the audible smoke alarm (horn)

is temporarily disabled for approximately 8 minutes while

smoke condition is being detected. A visual smoke alarm will

remain (LED flashing) during MUTE mode. A high smoke

voltage reference will also be activated at this time.

Simultaneous smoke and high smoke sampling will allow the

unit to enable the horn driver in case a high smoke condition

occurs during MUTE where the high smoke threshold is

crossed.

The MUTE mode can be overridden by the following

conditions: 1) a no smoke condition is detected, 2) high

smoke level detected, 3) remote smoke detected through I/O,

4) reset through test Button, 5) timeout of 8 minute window.

To help prevent a jammed Mute Button condition, the divider

string on the Mute Button should include a resistor to VDD,

R15 (around 10 MΩ) and a resistor R16 (4.7 MΩ) and

capacitor, C7 (0.047 mF) in series to VSS.

CALIBRATION

To facilitate checking the sensitivity and calibrating smoke

detectors, the MC146010 can be placed in Calibration mode.

In this mode, certain device pins are controlled/reconfigured

as shown in Table 4. To place the part in Calibration mode,

Pin 16 (Test/ Mute) must be pulled below VSS pin with 100 µA

continuously drawn out of the pin for at least one cycle of the

OSC pin. To exit this mode, the Test/ Mute pin is floated for at

least one OSC cycle.

In the Calibration mode, the IRED pulse rate is increased.

An IRED pulse occurs every clock cycle. Also, Strobe is

always Active Low. It is recommended to short R12 (Figure 5)

in this mode. This will allow for a similar recovery of the

emitter circuitry as in normal operation. Pin 1, pin 2, and

pin 12 should be buffered with a unity gain amplifier to

measure their outputs.

MC146010

10

Sensors

Freescale Semiconductor

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