A5303SLETR-T - Allegro Microsystems

Description

The A5303 is a low-current BiCMOS photoelectric smoke

detector circuit with ultra-low standby current and can operate

for 10 years powered by inexpensive batteries. This device can

be used with an infrared optical chamber to sense light scattered

from smoke particles. A networking capability allows units to

be interconnected so that if any unit senses smoke all units will

sound an alarm. Special features are incorporated in the design

to facilitate calibration and testing of the finished detector.

A variable-gain photoamplifier can be directly interfaced to

an infrared emitter-detector pair. The amplifier gain levels

are determined by two external capacitors and are internally

selected depending on the operating mode. Low gain is selected

during standby and timer modes. During a local alarm, this low

gain is increased (internally) by approximately 45% to provide

hysteresis. High gain is used during pushbutton test and to

periodically monitor the chamber sensitivity during standby.

The internal oscillator and timing circuitry minimize standby

power by sensing for smoke for only 100 μs once every 10 s.

A special three-stage-speedup sensing scheme is incorporated

to minimize the time to an audible alarm and also to reduce

false triggering. Chamber sensitivity is periodically monitored

and two consecutive cycles of degraded sensitivity are required

for a warning signal to occur.

The A5303 is supplied in a thin profile (<1.2 mm overall

height) 20-pin TSSOP package (0.65 mm nominal lead pitch).

The package is lead (Pb) free with 100% matte tin leadframe

plating.

5303-DS

Features and Benefits

▪ Low average standby current allows 10-year battery life

▪ 2.3 to 5.5 V operating range

▪ Interconnect option

▪ Logic outputs to control an external sound IC

▪ Low battery detection and warning

▪ Chamber sensitivity test and warning

▪ Triple horn-chirp to distinguish chamber warning

▪ Power-on reset (POR)

▪ Digital filter on I/O provides significant noise immunity

▪ Timer (hush) mode for enabling reduced sensitivity period

▪ Built-in circuits to reduce false triggering

▪ ESD protection circuitry on all pins

▪ Temporal Horn Pattern, per UL217, NFPA72, ISO8201

▪ Latching alarm indicator identifies alarm-initiating devices

Photoelectric Smoke Detector

with Interconnect, Timer, and Latching Alarm Indicator

Package: 20-pin TSSOP (suffix LE)

Not to scale

A5303

Typical Application Diagram

Control

Logic

SOUT0

VDD

TEST

56 nF

5.6 nF

DETECT

Gain

Select

STROBE

IRED

OSC

Timing

Low Batt

1.2 V

3 V

100 F

LED

VSS

560 

200 k

10 F

1.6 V

OSCCAP

1500 pf

Push-to-test

HUSH

Connect HUSH to

VSS to disable

timer mode

Connect to allow timer (hush) mode operation

ISET

LVSET

Low Batt

Sample

A resistor connected

between this pin and

VDD or VSS adjusts

the low-battery threshold

SOUT1 Voice IC outputs

10 100 k

SOUT2

TRES

I/O

220 

To / from

other units

BLINK

In standby, BLINK = VDD

causes LED to blink,

BLINK = VSS causes

LED not to blink

HORN

Output to optional

boost converter to

drive a piezo horn

Smoke

Chamber

Red LED

5 k 

3 k

3 

1 k 

Photoelectric Smoke Detector

with Interconnect, Timer, and Latching Alarm Indicator

A5303

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Selection Guide

Part Number Pb-free and RoHS Package Packing

A5303SLE-T Yes 20-pin TSSOP (JEDEC MO-153AC) 75 pieces / tube

A5303SLETR-T Yes 20-pin TSSOP (JEDEC MO-153AC) 4000 pieces / reel

Absolute Maximum Ratings

Characteristic Symbol Notes Rating Units

Supply Voltage Range VDD Referenced to VSS –2.3 to 6 V

DC Input Voltage Range VIN Referenced to VSS –0.3 to 6 V

Operating Ambient Temperature Range TAAllegro Range S –20 to 85 ºC

Maximum Junction Temperature TJ(max) 150 ºC

Storage Temperature Range Tstg –55 to 150 ºC

Pin-out Diagram

Thermal Characteristics

Characteristic Symbol Test Conditions* Value Units

Package Thermal Resistance RJA Estimated, single-layer PCB, minimal exposed copper area 127 ºC/W

*Additional thermal information available on Allegro website.

Terminal List

Number Name Function

1 SOUT1 Logic push-pull output for controlling an external sound IC

2 SOUT0 Logic push-pull output for controlling an external sound IC

3 I/O Input-output to interconnected detectors

4 BLINK Logic input for enabling/disabling the LED blink during standby

5 HUSH Input for photoamplifier timer mode reference; can also disable timer mode

6 ISET A resistor on this pin connected to VSS sets the IRED output current

7 VDD Positive supply voltage

8 IRED Terminal to drive smoke chamber IR LED

9 STROBE Strobed supply (VDD – 2 V) for photoamplifier low-side reference

10 DETECT Photoamplifier input

11 C2 Sets photoamplifier gain in standby mode

12 C1 Sets photoamplifier gain in supervisory mode

13 LVSET Optionally used with a resistor to adjust the low-battery threshold

14 TRES Connection for resistor to set clock times/frequency

15 VSS Negative supply voltage

16 OSC CAP Connection for capacitor and resistor to set clock times/frequency

17 TEST Enables push-to-test mode; starts timer mode, if enabled

18 HORN Logic output which optionally enables a boost converter to drive a horn

19 LED Output to drive visible LED

20 SOUT2 Logic push-pull output for controlling an external sound IC

SOUT1

SOUT0

I/O

BLINK

HUSH

ISET

VDD

IRED

STROBE

DETECT

SOUT2

LED

HORN

TEST

OSC CAP

VSS

TRES

LVSET

Photoelectric Smoke Detector

with Interconnect, Timer, and Latching Alarm Indicator

A5303

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

DC ELECTRICAL CHARACTERISTICS1 Valid at TA = 25°C, VDD = 2.3 to 5.5 V, configured as in Typical Application Diagram

(unless otherwise noted)

Characteristics Symbol Test Conditions Min. Typ.2Max. Unit

Supply Voltage Range VDD Operating 2.3 3.0 5.5 V

Operating Supply Current IDD

During standby, STROBE off – 2.3 5.0 A

During STROBE on, IRED off – 210 300 A

During STROBE on, IRED on – 220 300 A

Input Current IIN

BLINK, C1, C2, DETECT, OSC CAP, TRES

(pulldown off) –100 0 100 nA

TEST Pulldown Current IIN(TEST) VTEST = VDD = 3 V – 3.5 – A

Logic Voltage Low VI(L) ––

VDD ×

0.3 V

Logic Voltage High VI(H)

VDD ×

0.7 –– V

Strobe Output Voltage VST

Inactive – VDD –V

Active, IO = 100 to 500 A VDD –

2.1

VDD –

2.0

VDD –

1.9 V

Line Regulation VST(VDD) Active, VDD = 2.3 to 5.5 V – –60 – dB

Strobe Temperature Coefficient ST VSTROBE, VDD = 2.3 to 5.5 V – 0.01 – % / °C

Maximum IRED Current Setting IIRED(MAX)

Current is set by selection of resistor on ISET

pin – – 300 mA

IRED Current IIRED RISET = 3 89 100 111 mA

IRED Temperature Coefficient IRED IIRED, VDD = 2.3 to 5.5 V – 0.40 – % / °C

LED Drive Current ILED VLED = 0.5 V 0.6 1.2 1.8 mA

Low-Battery Warning Threshold VDD(th) LVSET open 2.4 2.5 2.6 V

Low-Battery Warning Minimum VDD(warn) VDD voltage guaranteed to operate SOUTx pins 1.8 V

Common Mode Voltage VIC Photoamplifier input VDD –

1.0 –VDD –

0.3 V

Smoke Comparator Reference Voltage VREF Any alarm condition, except hush mode – VDD –

1.6 –V

I/O Input Impedance ZI/O(in) No alarm conditions 40 83 – k

I/O Output Impedance ZI/O(out) Local or test alarm – 3.9 5.7 k

1Limits over the operating temperature range are based on characterization data. Characteristics are production tested at 25°C only.

2Typical values are at 25°C and are given for circuit design information only.

Photoelectric Smoke Detector

with Interconnect, Timer, and Latching Alarm Indicator

A5303

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Continued on the next page…

AC ELECTRICAL CHARACTERISTICS1 Valid at TA = 25°C, VDD = 2.3 to 5.5 V, configured as in Typical Application Diagram

(unless otherwise noted)

Characteristics Symbol Test Conditions OSC

Count Min. Typ.2Max. Unit

Oscillator Period tosc 1 9.4 10.5 11.5 ms

Smoke Check tsmoke 210 9.6 10.75 11.9 s

Low Battery Test tbattery No low-battery detected 218 41.3 45.9 50.5 min

tbattery2 Low-battery detected 212 39 43 48 s

Degraded Chamber Test tchamber No degraded chamber detected 218 41.3 45.9 50.5 min

tchamber2 Degraded chamber detected 212 39 43 48 s

LED Pulse Period

tled0 No local or remote smoke, BLINK = VSS – –

LED

Pulses

––

tled1 No local or remote smoke, BLINK = VDD 212 39 43 48 s

tled3 Local smoke 48 0.45 0.50 0.55 s

tled4 Remote smoke only – –

LED

Pulses

––

tled6 Pushbutton test, induced alarm 48 0.45 0.50 0.55 s

tled7 Timer mode, no alarm 210 9.67 10.75 11.83 s

LED Pulse Width tw(led) 1 9.5 10.5 11.5 ms

LED Pulse Spacing tsp(led) 3 pulses, degraded chamber 260.60 0.67 0.74 s

STROBE Pulse Period

tst1 No local or remote smoke 210 9.6 10.75 11.9 s

tst2 After 1 of 3 valid samples 192 1.8 2.0 2.2 s

tst3 After 2 of 3 valid samples and during local alarm 96 0.8 1.0 1.1 s

tst4 Remote smoke only 768 7.2 8.0 8.9 s

tst5 Chamber test, no local alarm 218 41.3 45.9 50.5 min

tst6 Pushbutton test, induced alarm 24 225 252 278 ms

STROBE Pulse Width tw(st) 1 9.5 10.5 11.5 ms

IRED Pulse Period

tired1 No local or remote smoke 210 9.6 10.75 11.9 s

tired2 After 1 of 3 valid samples 192 1.8 2.0 2.2 s

tired3 After 2 of 3 valid samples and during local alarm 96 0.8 1.0 1.1 s

tired4 Remote smoke only 768 7.2 8.0 8.9 s

tired5 Chamber test, no local alarm 218 41.3 45.9 50.5 min

tired6 Pushbutton test, induced alarm 24 225 252 278 ms

IRED Pulse Width tw(ired) 0.01 94 105 116 s

I/O to Active Delay td(io) Local alarm – – 0 – s

I/O Charge Dump Duration tdump End of local alarm or test 96 0.9 1.0 1.1 s

Rising Edge on I/O to Alarm tr(io) No local alarm 9 to 13 9 ×

tosc

94.5 –

137

13 ×

tosc ms

Photoelectric Smoke Detector

with Interconnect, Timer, and Latching Alarm Indicator

A5303

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

SOUTx Output Warning Period tsoutx Low supply or degraded chamber 212 38.9 43 47.1 s

SOUTx Output Warning Pulse Width tw(soutx) Low supply or degraded chamber 1 9.5 10.5 11.5 ms

Horn Warning Pulse Period thorn Low battery or degraded chamber 212 38.9 43 47.1 s

Horn Warning Pulse Width tw(horn) Low battery or degraded chamber 1 9.5 10.5 11.5 ms

Horn Warning Pulse Spacing tsp(horn) 3 chirps, degraded chamber 260.60 0.67 0.74 s

Horn On-Time ton(horn) Local, remote, or test alarm 48 450 500 550 ms

Horn Off-Time

toff1(horn)

Local, remote, or test alarm (see Timing

Diagrams section) 48 450 500 550 ms

toff2(horn)

Local, remote, or test alarm (see Timing

Diagrams section) 144 1350 1500 1650 ms

Timer Mode Duration ttimer 57344 9.0 10.0 11.0 min

Failed Push-Test Indication on SOUTx tFAIL After TEST input goes low 211 to

3072

211 ×

tosc

21.5 –

32.3

3072 ×

tosc

1Limits over the operating temperature range are based on characterization data. Characteristics are production tested at 25°C only.

2Typical values are at 25°C and are given for circuit design information only.

AC ELECTRICAL CHARACTERISTICS (continued)1 Valid at TA = 25°C, VDD = 2.3 to 5.5 V, configured as in Typical Application

Diagram (unless otherwise noted)

Characteristics Symbol Test Conditions OSC

Count Min. Typ.2Max. Unit

Photoelectric Smoke Detector

with Interconnect, Timer, and Latching Alarm Indicator

A5303

Allegro MicroSystems, Inc.

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 of the

photoamplifier, Ae , 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 μF, but it should be selected

based on the photochamber background reflections reaching the

detector and the required level of sensitivity. Ae = 1 + (C1

/ 12),

where C1 is in pF. Ae should not exceed 10,000 and thus C1

should not exceed 0.1 μF. 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 of the

photoamplifier, Ae, 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. Ae = 1 + (C2

/ 12), where C2 is in pF. Ae should not

exceed 10,000 and thus C2 should not exceed 0.1 μF. This gain

increases by a nominal 45% 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 VDD – 2 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,

typically 3 V.

LVSET Pin

This pin allows the user to externally adjust the low-battery

alarm threshold. To increase the threshold, a resistor can be con-

nected between LVSET and VDD. To decrease the threshold, a

resistor can be connected between LVSET and VSS.

IRED Pin

This output provides a pulsed drive current for the external IR

emitter. To minimize noise impact, the IRED is not active when

the visible LED output is active.

ISET Pin

This pin allows the user to externally set the IRED current by

connecting a resistor between it and VSS. The IRED current

controls the amount of light generated by the IR LED in the

chamber. The IRED current, in mA, can be approximated using

the following equation:

IRED (mA) = 300 / RISET (1)

The chosen resistor should set a maximum of 300 mA (typically

a minimum of 1Ω).

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

alarm indicators. As an input, this pin is sampled every 4 clock

cycles (nominally 43 ms) during standby, and two consecutive

samples and one additional clock with I/O high are required

before signaling an alarm. If the I/O line goes low at all during

the 96.8 ms, the remote alarm is not enabled, providing sig-

nificant immunity to I/O noise and other pulses on the I/O line

which are shorter than 9 clock cycles. 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 a large (distributed) 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.

SOUT0, SOUT1, SOUT2 Pins

These pins provide push-pull CMOS logic outputs to control an

external sound IC. The outputs indicate the state of the device as

follows:

Condition SOUT2 SOUT1 SOUT0

Standby L L L

Local Alarm L L H

Remote Alarm L H L

Push-Test Passed L H H

Push-Test Failed H L L

Low-Battery H L H

Degraded Chamber H H L

Photoelectric Smoke Detector

with Interconnect, Timer, and Latching Alarm Indicator

A5303

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

HORN Pin

The HORN pin is a logic output provided to enable an optional,

external boost converter that can drive a piezoelectric (piezo)

horn. Using a boost converter to drive a piezo horn allows alarms

to generate high SPL levels from low supply voltages. HORN will

be driven high to enable the boost converter. The output of the

boost converter will be connected to the piezo horn such that the

horn will sound when the converter is enabled. If a boost con-

verter and horn are not used, this pin should be left open.

BLINK Pin

This logic input determines the LED operation while the device is

in standby. If BLINK is connected to VDD the device will blink

once every approximately 43 s in standby. If BLINK is connected

to VSS the device will not blink in standby. If a low-battery or

degraded-chamber condition exists while the device is in standby,

the LED will blink as described in the Alarm Indications section,

regardless of the state of the BLINK pin. The BLINK pin has no

effect when the device is in local, remote, or test alarm.

LED Pin

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

LED. The LED indicates detector status as follows (with compo-

nent values as in the typical application, all times nominal):

Condition Pulse Occurrence

Standby, BLINK = VDD Every 43.0 s

Standby, BLINK = VSS No LED pulses

Local Smoke Every 0.5 s

Remote Alarm No pulses

Test Mode Every 0.5 s

Timer (Hush) Mode Every 10.8 s

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, which is also

the STROBE pulse width. The internal clock low time can be

calculated by:

low = 0.693 × ROSCCAP × COSCCAP (2)

TRES (Timing Resistor) Pin

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

nal oscillator and sets the internal clock high time, which is also

the IRED pulse width. With component values shown, this time is

nominally 105 μs. The internal clock high time can be calculated

by:

high = 0.693 × RTRES × COSCCAP (3)

VSS Pin

This pin is connected to the negative supply potential (usually

ground).

HUSH Pin

This input pin 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. Timer mode allows the user to temporarily

hush alarms caused by nuisance smoke or steam (such as from

cooking).

When the voltage on this pin is greater than approximately

50 mV, entering timer mode is enabled, and a high-to-low transi-

tion on the TEST pin resets and starts timer mode. If use of timer

mode is not desired this pin must be connected to VSS, and timer

mode is disabled.

During timer mode the smoke comparator reference is established

externally by a resistive divider (R1 and R2) between VDD and

STROBE. Also, during timer mode the photoamplifier gain, Ae,

is internally reduced to about 55% that during the normal-gain

mode. Thus, Ae = 1 + (C2 / 22), where C2 is in pF. These two

conditions allow the detector to operate with reduced sensitivity

during timer mode. If the level of smoke increases such that the

temporary alarm threshold is reached, a local alarm will sound. If

the HUSH pin is connected directly to STROBE without using a

resistor divider, then a local alarm will never occur during timer

mode, regardless of the smoke level. When not in timer mode,

the smoke comparator reference is set internally to approximately

VDD – 1.6 V.

The resistor dividers formed by the adjustable photoamp-divider

and the HUSH divider (R1 + R2, if timer mode is used) should

be chosen so that the load on STROBE does not exceed 500 μA.

Thus, the photoamp-divider (8 kΩ in the typical application) in

parallel with the HUSH divider (R1 + R2) shall be no

less than 4 kΩ.

TEST Pin

This pin has an internal pulldown device and is used to manually

invoke push-to-test mode and timer mode. Push-to-test mode is

initiated by a voltage greater than approximately VDD – 0.5 V

on this pin (usually the closure of a normally open push-button

switch to VDD). After one oscillator cycle, the amplifier gain is

Photoelectric Smoke Detector

with Interconnect, Timer, and Latching Alarm Indicator

A5303

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

increased by internal selection of C1 so that background reflec-

tions in the smoke chamber can be used to simulate a smoke con-

dition, and IRED pulses every 252 ms (nominal). After the third

IRED pulse (three consecutive simulated smoke conditions), the

successful test signals a continuous passing-test-alarm condition

to the sound IC, outputs the temporal pattern to the piezo horn,

and activates the I/O pin. When the pushbutton is released, the

input returns to VSS due to the internal pulldown. After one oscil-

lator 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. The high-to-low

transition also resets the latching alarm indicator, if it is latched.

If the chamber malfunctions or is too dirty, the push-test will fail

to simulate a smoke condition, and after three failed STROBE

pulses the device signals a continuous failing-test-alarm condi-

tion on the SOUTx pins. The piezo driver and the I/O pins are not

enabled.

Diagnostic Test/Calibration mode is available to facilitate calibra-

tion and test of the IC and the assembled detector. It is initiated

by pulling TEST below VSS by continuously drawing 200 μA

from the pin for at least one clock cycle on OSC CAP. The cur-

rent should not exceed 500 μA and under these conditions,

TEST pin voltage will clamp at approximately 250 mV below

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

15 kΩ resistor. In this mode, certain device pins are reconfigured

as described in table 1. The IRED pulse rate is 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 VSS, for at least one OSC CAP cycle.

Latching Alarm Indicator

When multiple smoke detectors are networked through the I/O

line, the latching alarm indicator allows the user to identify which

detector(s) initiated an alarm. When a local alarm condition

occurs, the initiating detector(s) will latch the event in memory.

After the alarm condition has expired (the device stops signaling

the alarm condition to the sound IC) the initiating detector(s) will

output an additional 10 ms LED pulse every 43 seconds. If the

BLINK pin is connected to VDD, the additional pulse will occur

0.67 seconds after the normal standby pulse. The user can clear

the latched alarm condition by pressing and releasing the push-to-

test button. If the user does not press the push-to-test button, the

latched alarm condition will cease after 24 hours to preserve bat-

tery life, and to prevent masking future latched alarm indications.

Alarm Indications

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

low battery, and degraded chamber sensitivity. These are indi-

cated by a combination of SOUTx output, piezo horn, and LED

signals, which continue until the alarm condition is resolved.

A local alarm always overrides a remote alarm and a push-test.

Remote alarm always overrides a push-test. A local alarm, remote

alarm, or a push-test will inhibit warning signals for low battery

or degraded chamber.

During a local or a remote alarm condition, the device continu-

ously signals an alarm condition on the SOUTx pins that indi-

cates the type of the alarm. The piezo 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

also distinguishes a local alarm from a remote alarm. During a

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 the BLINK 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. If this

pin is high, supervisory gain is selected.

NOTE: If I/O is low, clocking this pin will cause the

device to exit diagnostic/calibration mode and enter an

Allegro-defined test mode.

BLINK If the I/O pin is high, this pin is reconfigured as the

photoamplifier output.

SOUT0 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 45% (hysteresis).

SOUT2 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 VDD falls below the

low-battery threshold, the output turns on.

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.

Photoelectric Smoke Detector

with Interconnect, Timer, and Latching Alarm Indicator

A5303

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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

45.9 min). 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 background

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

dirty, or obstructed chamber prevents this during a test, the test

period decreases to 43 s. After two consecutive failed tests, the

device signals a degraded chamber condition to the sound IC.

It also chirps the horn and pulses the LED three times every

43 seconds. The condition is resolved when the chamber is either

cleared or cleaned, and the test period then reverts to (nominally)

45.9 min.

The low-battery test also occurs periodically (also nominally

every 45.9 min, but at a different time than the degraded-chamber

test). During this test a resistive divider off VDD is compared to

an internal band-gap reference. If VDD is below the threshold, the

device signals a low battery condition to the sound IC and the

test period decreases to 43 s. It also chirps the horn and pulses the

LED once every 43 seconds. The condition is resolved when the

battery is replaced and the test period then reverts to (nominally)

45.9 min.

Photoelectric Smoke Detector

with Interconnect, Timer, and Latching Alarm Indicator

A5303

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Timing Diagrams

(Not to Scale)

OSC CAP

STROBE

IRED

Internal clock

Standby Mode

SOUTx

VDD

Chamber

sensitivity

Photo sample

Chamber test

Low-battery test

Chamber test

LED

SOUTx

Low Battery Condition

Degraded Chamber Condition

osc

w(st)

w(led)

w(horn)

horn

soutx

smoke

, t

st1

, t

ired1

chamber

, t

st5

, t

ired5

battery

, t

led0

, t

st5

, t

ired5

(Low battery)

(Degraded chamber)

Test event

HORN

horn

SOUT(2:0) = (HHL)

SOUT(2:0) = (HLH)

soutx

sp(horn)

w(horn)

w(soutx)

chamber2

battery2

w(soutx)

LED

led1

w(horn)

LED,

BLINK = V

led1

chamber

these two pulses will not exist if BLINK = V

sp(led)

chamber

w(led)

battery

LED,

BLINK = V

(LED OFF)

battery2

w(ired)

Photoelectric Smoke Detector

with Interconnect, Timer, and Latching Alarm Indicator

A5303

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

HORN

Local Smoke Detection Condition

ton(horn) toff1(horn)

toff2(horn)

I/O

tst2,ired2 tst3,ired3

tst3,ired3

tw(led)

3rd strobe without smoke1st strobe with smoke 3rd strobe with smoke

STROBE

IRED

tw(st)

tdump

pmud egrahc O/I)TUPTUO(

Remote Alarm Condition

(INPUT)

HORN

I/O

ton(horn) toff1(horn)

toff2(horn)

tr(io)

tw(st)

STROBE

tst4,ired4

tled3

SOUTx

SOUT(2:0) = (LLH)

SOUTx

SOUT(2:0) = (LHL)

Chamber

(smoke present)

LED

BLINK = V

or V

(LED OFF)

LED

BLINK = V

or V

Photoelectric Smoke Detector

with Interconnect, Timer, and Latching Alarm Indicator

A5303

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Test Alarm Mode (passing)

LED

BLINK = V

or V

HORN

I/O

STROBE

TEST

dump

I/O charge dump

on(horn)

off1(horn)

off2(horn)

st6,ired6

(OUTPUT)

w(st)

w(led)

led6

SOUTx

SOUT(2:0) = (LHH)

Test Alarm Mode (failing)

LED

BLINK = V

or V

HORN

I/O

STROBE

TEST

w(st)

w(led)

SOUTx

SOUT(2:0) = (HLL)

FAIL

Photoelectric Smoke Detector

with Interconnect, Timer, and Latching Alarm Indicator

A5303

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Package LE, 20-Pin TSSOP

1.20 MAX

0.15

0.00

0.30

0.19

0.20

0.09

8º

0º

0.60 ±0.15

1.00 REF

SEATING

PLANE

C0.10

20X

0.65 BSC

0.25 BSC

6.50±0.10

4.40±0.10 6.40±0.20

GAUGE PLANE

SEATING PLANE

ATerminal #1 mark area

For Reference Only; not for tooling use (reference MO-153 AC)

Dimensions in millimeters

Dimensions exclusive of mold flash, gate burrs, and dambar protrusions

Exact case and lead configuration at supplier discretion within limits shown

0.45

1.70

Reference land pattern layout (reference IPC7351

SOP65P640X110-21M);

All pads a minimum of 0.20 mm from all adjacent pads; adjust as

necessary to meet application process requirements and PCB layout

tolerances; when mounting on a multilayer PCB, thermal vias at the

exposed thermal pad land can improve thermal dissipation (reference

EIA/JEDEC Standard JESD51-5)

PCB Layout Reference View

6.10

0.65

Photoelectric Smoke Detector

with Interconnect, Timer, and Latching Alarm Indicator

A5303

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

For the latest version of this document, visit our website:

www.allegromicro.com

Allegro MicroSystems offers an industry-leading range of ionization

and photoelectric smoke detector ICs. For a current listing, please visit

our website at:

www.allegromicro.com

The products described herein are manufactured under one or more of the following U.S. patents: 5,045,920; 5,264,783; 5,442,283; 5,389,889;

5,581,179; 5,517,112; 5,619,137; 5,621,319; 5,650,719; 5,686,894; 5,694,038; 5,729,130; 5,917,320; and other patents pending.

Allegro MicroSystems, Inc. reserves the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be required to per-

mit improvements in the per for mance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the

information being relied upon is current.

Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the

failure of that life support device or system, or to affect the safety or effectiveness of that device or system.

The in for ma tion in clud ed herein is believed to be ac cu rate and reliable. How ev er, Allegro MicroSystems, Inc. assumes no re spon si bil i ty for its use;

nor for any in fringe ment of patents or other rights of third parties which may result from its use.