A5366CA Datasheet A5366CA, A5366CA-T, A5366CLWTR-T | P7-P9

Photoelectric Smoke Detector

with Interconnect and Timer

A5366

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Pin and Circuit Description

(In Typical Application)

C1 Pin

A capacitor connected to this pin determines the gain, A

, of

the photoamplifier during the push-to-test mode and during the

chamber monitor test. A typical capacitor value for this high-

gain (supervisory) mode is 0.047 F, but it should be selected

based on the photochamber background reflections reaching the

detector and the desired level of sensitivity. A

= 1 + (C

/ 10),

where C

is in pF. A

should not exceed 10,000 and thus C

should not exceed 0.1 F. Coupling of other signals to the C1,

C2, and DETECT inputs must be minimized.

C2 Pin

A capacitor connected to this pin determines the gain, A

, of

the photoamplifier during standby. A typical capacitor value for

this low-gain mode is 4700 pF, but it should be selected based

on a specific photochamber and the desired level of sensitiv-

ity to smoke. A

= 1 + (C

/ 10), where C

is in pF. A

should not

exceed 10,000 and thus C

should not exceed 0.1 F. This gain

increases by a nominal 10% after a local alarm is detected (three

consecutive detections). A resistor must be installed in series

with the C2 capacitor.

DETECT Pin

This is the input to the photoamplifier and is connected to the

cathode of the photodiode. The photodiode is operated at zero

bias and should have low dark leakage current and low capaci-

tance. A shunt resistor must be installed in parallel with the

photodiode.

STROBE Pin

This output provides a strobed, regulated voltage of V

– 5 V.

The minus side of all internal and external photoamplifier cir-

cuitry is referenced to this pin.

VDD Pin

This pin is connected to the positive supply potential and can

range from 6 to 12 V with respect to V

IRED Pin

This output provides a pulsed base current for the external NPN

transistor, which drives the IR emitter. Its beta should be greater

than 100. To minimize noise impact, the IRED output is not

active when the horn and visible LED outputs are active.

I/O Pin

A connection at this pin allows multiple smoke detectors to be

interconnected. If any single unit detects smoke, its I/O pin is

driven high, and all connected units will sound their associated

horns.

As an input, the I/O is sampled every fourth clock cycle (nomi-

nally 42 ms). When the I/O pin is driven high by another device,

three consecutive samples with I/O high plus one additional

cycle (nominally 10.5 ms) are required to cause an alarm. If the

I/O falls below its threshold at any time during those (nomi-

nally) 95 ms, an internal latch is reset and there will not be an

alarm. Thus, depending on when during the (nominally) 42 ms

sample cycle I/O is initially forced high, the I/O must remain

high for a minimum of (nominally) 95 to 137 ms to cause an

alarm. This filtering provides significant immunity to I/O noise.

The LED is suppressed when an alarm is signaled from an

interconnected unit, and any local alarm condition causes this

pin to be ignored as an input. An internal NMOS device acts as

a charge dump to aid in applications involving large (distrib-

uted) capacitance, and is activated at the end of a local or test

alarm. This pin has an on-chip pull-down device and must be

left unconnected if not used. In the application, there should be a

series current-limiting resistor to other smoke alarms.

HORN1, HORN2, FEEDBACK Pins

These three pins are used with a self-resonating piezoelectric

transducer and horn-starting external passive components. The

output HORN1 is connected to the piezo metal support elec-

trode. The complementary output, HORN2, is connected to the

ceramic electrode. The FEEDBACK input is connected to the

feedback electrode. If the FEEDBACK pin is not used, it must

be connected to VSS.

LED Pin

This open-drain NMOS output is used to directly drive a visible

LED. The load for the low-battery test is applied to this output.

If an LED is not used, it should be replaced with an equivalent

resistor (typically 500 to 1000 ) such that the battery load-

ing remains about 10 mA. The low-battery test does not occur

coincident with any other test or alarm signal. The LED also

indicates detector status as follows (with component values as in

the typical application, all times nominal):

Condition Pulse Occurrence

Standby Every 43 s

Local Smoke Every 0.5 s

Remote Alarm No pulses

Test Mode Every 0.5 s

Timer Mode Every 10 s

Photoelectric Smoke Detector

with Interconnect and Timer

A5366

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

OSC CAP (Oscillator Capacitor) Pin

A capacitor between this pin and VDD, along with a parallel

resistor, forms part of a two-terminal oscillator and sets the inter-

nal clock low time. With component values shown, this nominal

time is 10.4 ms and essentially the oscillator period. The internal

clock low time can be calculated by:

low

= 0.693 × R

OSCCAP

× C

OSCCAP

TIMING RES (Timing Resistor) Pin

A resistor between this pin and OSC CAP is part of the two-

terminal oscillator and sets the internal clock high time, which is

also the IRED pulse width. With component values shown, this

time is nominally 105 s. The internal clock high time can be

calculated by:

high

= 0.693 × R

TIMINGRES

× C

OSCCAP

VSS Pin

This pin is connected to the negative supply potential (usually

ground).

HUSH Pin

This input pin has an internal pull-down device and serves two

purposes in standby mode. It serves to enable/disable entering

the internal 10-minute (nominal) “hush” timer mode, and also

as the reference for the smoke comparator during timer mode.

When the voltage on this pin is greater than 1.5 V, entering timer

mode is enabled, and a high-to-low transition on the TEST pin

resets and starts timer mode. If use of timer mode is not desired,

this pin can be connected to VSS or left open, and a voltage

of less than 0.5 V on the pin will disable timer mode. During

timer mode, the smoke comparator reference is established by a

resistive divider (Rx1 and Rx2) between the VDD and STROBE

pins and allows the detector to operate with reduced sensitivity

during timer mode. This allows the user to hush alarms caused

by nuisance smoke or steam (such as from cooking). When not

in timer mode, the smoke comparator reference is set internally

to approximately V

– 3.5 V.

TEST Pin

This pin has an internal pull-down device and is used to manu-

ally invoke two test modes and timer mode.

Push-to-Test mode is initiated by a voltage greater than approxi-

mately V

– 0.5 V on this pin (usually the depression of a

normally-open pushbutton switch to VDD). After one oscilla-

tor cycle, the amplifier gain is increased by internal selection

of C1 so that background reflections in the smoke chamber can

be used to simulate a smoke condition, and IRED pulses every

252 ms (nominal). After the third IRED pulse (three consecu-

tive simulated smoke conditions), the successful test activates

Table 1. Alternate Pin Configuration During Diagnostic

Test/Calibration Mode

Pin Name Alternate Configuration

I/O

Disabled as an output. A logic high on this pin places the

photoamplifier output on C1 or C2 as determined by the

HUSH pin. The amplifier output appears as pulses.

HUSH

If the I/O pin is high, this pin controls the amplifier gain

capacitor. If this pin is low, normal gain is selected and

the amplifier output is on pin C1. If this pin is high,

supervisory gain is selected and the amplifier output is

on C2.

NOTE: If I/O is low, four rising edges on this pin will

cause the device to exit diagnostic/calibration mode and

enter an Allegro-defined test mode.

FEED-

BACK

If the I/O pin is high and the HUSH pin is low (normal

gain), taking this pin to a high logic level increases the

amplifier gain by 10% (hysteresis).

OSC CAP

This pin may be driven by an external clock source.

Driving this pin low and high drives the internal clock low

and high. The external RC network may remain intact.

HORN1

This pin is reconfigured as the smoke integrator output.

Three consecutive smoke detections will cause this pin

to go high and three consecutive no-smoke detections

cause this pin to go low.

LED

This pin becomes a low-battery indicator. The open-drain

NMOS output is normally off. If V

falls below the low-

battery threshold, the output turns on.

the horn drivers and the I/O pin, and the LED blinks once every

0.5 s. If the test fails, the LED will not blink, the horn will not

sound, and the I/O pin will remain low. When the pushbutton is

released, the input returns to V

due to the internal pull down.

After one oscillator cycle, the amplifier gain returns to normal,

and after three additional IRED pulses (less than one second), the

device exits this mode and returns to standby. This high-to-low

transition on TEST also resets and starts the 10-minute (nominal)

“hush” timer mode, if the mode is enabled via the HUSH pin.

Diagnostic Test/Calibration Mode is available to facilitate

calibration and test of the IC and the assembled detector. It is

initiated by pulling TEST below V

by continuously drawing

400 A from the pin for at least one clock cycle on OSC CAP.

The current should not exceed 800 A and under these condi-

tions, TEST pin voltage will clamp at approximately 250 mV

below V

. One option is to connect TEST to a –5 V supply

through a 12 k resistor. In this mode, certain device pins are

reconfigured as described in table 1. The IRED pulse rate is

Photoelectric Smoke Detector

with Interconnect and Timer

A5366

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

increased to one pulse every OSC CAP cycle and the STROBE

pin is always active. To exit this mode, the TEST pin should be

floated, or returned to V

, for at least one OSC CAP cycle.

Alarm Indications

Alarm conditions include: local smoke detection, a remote alarm,

low battery, or degraded chamber sensitivity. These are indicated

by a combination of horn and LED signals, which continue until

the alarm condition is resolved. A local alarm always overrides

a remote alarm, and a local or remote alarm will inhibit warning

signals for low battery or degraded chamber.

During a local or a remote alarm condition, the horn output is a

continuous modulated tone (temporal horn pattern), nominally:

0.5 s on, 0.5 s off, 0.5 s on, 0.5 s off, 0.5 s on, and 1.5 s off. The

visible LED distinguishes a local alarm from a remote alarm.

During a local alarm, the LED blinks every 0.5 s (nominally), but

during a remote alarm, the LED is disabled and does not blink.

The degraded-chamber test occurs periodically (nominally every

43 s). During this test, the gain of the photoamplifier is switched

to the high (supervisory) level, set by C1. The device expects

that the photodiode will receive enough reflected background

light in the chamber to cause an alarm condition. If a faulty, dirty,

or obstructed chamber prevents this for two consecutive tests,

the device signals degraded chamber with one short (nominally

10 ms) horn chirp every 43 s, essentially halfway between LED

flashes. The condition is resolved when the chamber is either

cleared or cleaned.

The low-battery test also occurs periodically (also nominally

every 43 s, but offset from the degraded-chamber test). Dur-

ing this test, the load of the LED is applied to the battery, and

a resistive divider off V

is compared to an internal band-gap

reference. If V

is below the threshold, the device signals low

battery with one short (nominally 10 ms) horn chirp every 43 s,

occurring almost simultaneously with the visible LED flash. The

condition is resolved when the battery is replaced.

P1-P3 P4-P6 P7-P9 P10-P12 P13-P13

A5366CA

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