MPXM2102AS datasheet(644/670 Pages) MOTOROLA

644 / 670 page

MC145012

4–52

Motorola Sensor Device Data

www.motorola.com/semiconductors

VDD (Pin 5)

This pin is connected to the positive supply potential and

may range from + 6 to + 12 V with respect to V SS

CAUTION: In battery–powered applications, reverse–polar-

ity protection must be provided externally.

IRED (Pin 6)

This output provides pulsed base current for external NPN

transistor Q1 used as the infrared emitter driver. Q1 must

have

β ≥ 100. At 10 mA, the temperature coefficient of the

output voltage is typically + 0.5%/

°C from – 10° to 60°C. The

supply–voltage coefficient (line regulation) is

± 0.2%/V maxi-

mum from 6 to 12 V. The IRED pulse width (active–high) is

determined by external components R1 and C3. With a

100 k

Ω/1500 pF combination, the nominal width is 105 µs.

To minimize noise impact, IRED is not active when the vis-

ible LED and horn outputs are active. IRED is active near the

end of strobe pulses for smoke tests, chamber sensitivity

test, and pushbutton test.

I/O (Pin 7)

This pin can be used to connect up to 40 units together in

a wired–OR configuration for common signaling. VSS is used

as the return. An on–chip current sink minimizes noise pick

up during non–smoke conditions and eliminates the need for

an external pull–down resistor to complete the wired–OR.

Remote units at lower supply voltages do not draw excessive

current from a sending unit at a higher supply voltage.

I/O can also be used to activate escape lights, auxiliary

alarms, remote alarms, and/or auto–dialers.

As an input, this pin feeds a positive–edge–triggered flip–

flop whose output is sampled nominally every 1 second dur-

ing standby (using the recommended component values). A

local–smoke condition or the pushbutton–test mode forces

this current–limited output to source current. All input signals

are ignored when I/O is sourcing current.

I/O is disabled by the on–chip power–on reset to eliminate

nuisance signaling during battery changes or system power–

up.

If unused, I/O must be left unconnected.

BRASS (Pin 8)

This half of the push–pull driver output is connected to the

metal support electrode of a piezoelectric audio transducer

and to the horn–starting resistor. A continuous modulated

tone from the transducer is a smoke alarm indicating either

local or remote smoke. A short beep or chirp is a trouble

alarm indicating a low supply or degraded chamber sensitiv-

ity.

SILVER (Pin 9)

This half of the push–pull driver output is connected to the

ceramic electrode of a piezoelectric transducer and to the

horn–starting capacitor.

FEEDBACK (Pin 10)

This input is connected to both the feedback electrode of a

self–resonating piezoelectric transducer and the horn–start-

ing resistor and capacitor through current–limiting resistor

R4. If unused, this pin must be tied to VSS or VDD.

LED (Pin 11)

This active–low open–drain output directly drives an exter-

nal visible LED at the pulse rates indicated below. The pulse

width is equal to the OSC period.

The load for the low–supply test is applied by this output.

This low–supply test is non–coincident with the smoke tests,

chamber sensitivity test, pushbutton test, or any alarm sig-

nals.

The LED also provides a visual indication of the detector

status as follows, assuming the component values shown in

Figure 5:

Standby (includes low–supply and chamber sensitivity

tests) — Pulses every 32.4 seconds (typical)

Local Smoke — Pulses every 0.51 seconds (typical)

Remote Smoke — No pulses

Pushbutton Test — Pulses every 0.51 seconds (typical)

OSC (Pin 12)

This pin is used in conjunction with external resistor R2

(7.5 M

Ω) to VDD and external capacitor C3 (1500 pF) to VDD

to form an oscillator with a nominal period of 7.9 ms (typical).

R1 (Pin 13)

This pin is used in conjunction with resistor R1 (100 k

Ω) 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 deter-

mines 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 (Pin 16)

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

manually invoke a test mode.

The

Pushbutton Test mode is initiated by a high level at Pin

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

ton switch to VDD). After one oscillator cycle, 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 reflec-

tions 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 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.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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