General Description

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R&E International 

             

A Subsidiary of Microchip Technology Inc.

 

 

 
RE46C141 

CMOS Photoelectric Smoke Detector ASIC with Interconnect

 

Product Specification

 

© 2009 Microchip Technology Inc.                                                                                                                  DS22177B-page 1 
       

                                                                  

 

 

 
General Description 

 
The RE46C141 is low power CMOS photoelectric type 
smoke detector IC. With minimal external components 
this circuit will provide all the required features for a 
photoelectric type smoke detector. 
 
The design incorporates a gain selectable photo 
amplifier for use with an infrared emitter/detector pair. 
An internal oscillator strobes power to the smoke 
detection circuitry for 100us every 8.1 seconds to keep 
standby current to a minimum. If smoke is sensed the 
detection rate is increased to verify an alarm condition. 
A high gain mode is available for push button chamber 
testing. 
 
A check for a low battery condition and chamber 
integrity is performed every 32 seconds when in 
standby. The temporal horn pattern supports the NFPA 
72 emergency evacuation signal. 
 
An interconnect pin allows multiple detectors to be 
connected such that when one units alarms, all units 
will sound.  
 
The RE46C141 is recognized by Underwriters 
Laboratories for use in smoke detectors that comply 
with specification UL217 and UL268. 
 

 

Features 

 
•  Internal Power On Reset 

•  Low Quiescent Current Consumption 

•  Available in 16L PDIP, 16L N SOIC or 16L W SOIC 

•  ESD Protection on all Pins 

•  Interconnect up to 40 Detectors 

•  Temporal Horn Pattern 

•  Low Battery and Chamber Test 

•  Compatible with Motorola MC145012 

•  UL Recognized per File S24036 

•  Available in Standard Packaging or RoHS 

Compliant Pb Free Packaging. 

 

                Pin Configuration

 

 

 

 

 

 

 

 

 

16

1

TEST

C1 

 

 

 

 

 

2

LBSET

     C2

15

 

 

 

 

VSS

 

DETECT 

3

14

 

 

 

STROBE 

4

ROSC

13

 

 

ABSOLUTE MAXIMUM RATINGS 

 

 

 

PARAMETER SYMBOL 

VALUE 

UNITS 

Supply Voltage 

V

DD 

12.5 V 

Input Voltage Range Except FEED, IO 

V

in

 

-.3 to V

dd 

+.3 V 

FEED Input Voltage Range  

V

infd

  

-10 to +22 

IO Input Voltage Range 

V

io1

 

-.3 to 17 

Input Current except FEED 

I

in

 10 

mA 

Operating Temperature 

T

-25 to 75 

°C 

Storage Temperature 

T

STG

 

-55 to 125 

°C 

Maximum Junction Temperature 

T

J

 150 

°C 

 

Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device.   These are 
stress ratings only and operation at these conditions for extended periods may affect device reliability. 

 

This product utilizes CMOS technology with static protection; however proper ESD prevention procedures should be used when 
handling this product. Damage can occur when exposed to extremely high static electrical charge. 
 
 

 

 

 

COSC

5

12

VDD 

IRED 

IO 

HORNB 

 

 

 

LE

 

6

 

11

 

 

 

7

FEED

 

 

10

HORNS

 

 

8

9

 

 

 

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RE46C141 

CMOS Photoelectric Smoke Detector ASIC with Interconnect                             

        

R&E International

 

Product Specification                                                                                                          

A Subsidiary of Microchip Technology

 

Inc.

 

© 2009 Microchip Technology Inc.                                                                                                                  DS22177B-page 2 
       

                                                                  

 

 
 
 

DC Electrical Characteristics at TA = -25° to 75°C, VDD=9V, Typical Application (unless otherwise noted) 

Limits 

Parameter Symbol 

Test 

Pin Test 

Conditions 

Min Typ Max Units

Supply Voltage 

V

DD 

5 Operating 

6    12 V 

I

DD1 

Configured as in Figure 2, 
COSC=VSS 

 4 6 

uA 

I

DD2

 5 

Configured as in Figure 2, 
VDD=12V, COSC=VSS 

 5.5 8 uA 

I

DD3

 5 

Configured as in Figure 2, 
STROBE on, IRED off, VDD=12V 

  2 

mA 

Supply Current 

I

DD4

 5 

Configured as in Figure 2, 
STROBE on, IRED on, VDD=12V, 
Note 1 

  3 

mA 

V

IH1 

10 FEED 

6.2 4.5    V 

V

IH2

 

No Local Alarm, IO as an Input 

3.2 

 

 

Input Voltage High 

V

IH4

 16 

TEST 

8.5 

  V 

V

IL1 

10 FEED 

  4.5 2.7  V 

V

IL2

 

No Local Alarm, IO as an Input 

 

 

1.5 

Input Voltage Low 

V

IL4 

16 

TEST 

 

  

7  

I

IL1 

1,2,3 

VDD=12V, COSC=12V, STROBE 
active 

  

-100 

nA 

I

IL2

 12,15 

VDD=12V, 

Vin=VSS 

   

-100 

nA 

I

IL3

 16 

VDD=12V, 

Vin=VSS 

  

-1 

uA 

Input Leakage Low 

I

LFD 

10 FEED=-10V 

 

  -50 uA 

I

IH1 

1,2 

VDD=12V, Vin=VDD, STROBE 
active 

  

100 

nA 

I

IH2

 3,12,15 

VDD=12V, 

Vin=VDD 

   100 

nA 

Input Leakage High 

I

HFD 

10 FEED=22V 

 

  50 uA 

I

PD1

 16 

Vin=VDD 

.25 

 

10 

uA 

I

PDIO1

  7 Vin=VDD 

20  80 

uA 

Input Pull Down Current  

I

PDIO2

 7 

Vin=17V, 

VDD=12 

  

140 

uA 

Output Leakage Current 
Low 

I

OZL1

 

11,13 

Output Off, Output=VSS 

 

 

-1 

uA 

Output Leakage Current 
High 

I

OZH1

 

11,13 

Output Off, Output=VDD 

 

 

uA 

 

Note 1: Does not include Q3 emitter current.

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RE46C141 

CMOS Photoelectric Smoke Detector ASIC with Interconnect                             

        

R&E International

 

Product Specification                                                                                                          

A Subsidiary of Microchip Technology

 

Inc.

 

© 2009 Microchip Technology Inc.                                                                                                                  DS22177B-page 3 
       

                                                                  

 

 
 

DC Electrical Characteristics (continued) at TA= -25° to 75°, VDD=9V, Typical Application (unless 
otherwise noted)
 

Limits

 

Parameter Symbol 

Test 

Pin Test 

Conditions Min Typ Max Units

V

OL1 

8,9 Iol=16mA, 

VDD=6.5V 

 

  1  V 

V

OL2

 13 

Iol=5mA, 

VDD=6.5V 

 .5 

  V 

Output Voltage Low 

V

OL3

 11 

Iol=10mA, 

VDD=6.5V 

  

.6 

Output Voltage High 

V

Oh1 

8,9 Ioh=-16mA, 

VDD=6.5V 5.5 

 

 

I

IOH1

 

Alarm, Vio=Vdd-2V or Vio=0V 

-4 

 

-16 

mA 

Output Current 

I

IODMP

 7 

At Conclusion of Local Alarm or 
Test, Vio=1V 

5   mA 

Low Battery Alarm Voltage 

V

LB

 5 

R14=100K, 

R15=47K 

6.9 

7.2 

7.5 

V

STOF

 4 

STROBE off, VDD=12V, 
Iout=-1uA 

V

DD

 - 

.1 

  V 

V

STON

 4 

STROBE on, VDD=9V 
Iout= 100uA to 500uA 

V

DD

 - 

5.3 

V

DD

 -

V

DD

 -

4.7 

V

IREDOF

 

IRED off, VDD=12V, Iout=1uA 

 

 

.1 

Output Voltage 

V

IREDON

 6 

IRED on, VDD=9V 
Iout=0 to -6mA, Ta=25C 

2.25 3.1 3.75  V 

Common Mode Voltage 

V

CM1 

1,2,3 

Local smoke, Push to Test or 
Chamber Test, Note 1 

.5  

V

DD

-2 V 

Smoke Comparator 
Reference 

V

ref 

- Internal 

Reference 

V

DD

-

3.85 

 

V

DD

-

3.15 

TC

ST 

VDD=6V to 12V, STROBE Output 
Voltage 

 .01  %/ºC 

Temperature Coefficient 

TC

IRED 

VDD=6V to 12V, IRED Output 
Voltage 

 .3  

%/ºC 

ΔV

STON 

4,5 

Active, VDD=6V to 12V 

 

-50 

 

dB 

Line Regulation 

ΔV

IREDON

 

6,5 

Active, VDD=6V to 12V 

 

-30 

 

dB 

 

Note 1: Not production tested 
Typical values are for design information and are not guaranteed. 
Limits over the specified temperature range are not production tested and are based on characterization data. 
 

 

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RE46C141 

CMOS Photoelectric Smoke Detector ASIC with Interconnect                             

        

R&E International

 

Product Specification                                                                                                          

A Subsidiary of Microchip Technology

 

Inc.

 

© 2009 Microchip Technology Inc.                                                                                                                  DS22177B-page 4 
       

                                                                  

 

 
 

AC Electrical Characteristics at TA =-25° to 75°, VDD=9V, VSS=0V, Component Values from Figure 2 ; 
R9=100KΩ, R12=10MΩ, C5= 1.5nF(unless otherwise noted)
 

Limits 

Parameter Symbol 

Test 

Pin Test 

Conditions Min Typ Max Units

Oscillator Period 

T

POSC 

12 

No Alarm Condition, 

Note 2

 

7.1 7.9 8.6 mS 

LED and STROBE On Time 

T

ON1 

11,4 Operating 

7.1 7.9 8.6 mS 

T

PLED1 

11 

Standby, No Alarm 

28.8 

32.4 

35.2 

T

PLED2 

11 

Local Alarm Condition 

.45 

.5 

.55 

LED Period 

T

PLED4 

11 

Remote Alarm Only 

LED IS NOT ON 

T

PER1

 

4,6 

Standby, No Alarm 

7.3 

8.1 

8.8 

T

PER1A

 4,6 

Standby, After 1 Valid Smoke 
Sample 

1.8 2 2.2 S 

T

PER1B

 4,6 

Standby, After 2 Consecutive Valid 
Smoke Samples 

.9 1 1.1 S 

T

PER2

 4,6 

In Local Alarm – (3 Consecutive 
Valid Smoke  Samples) 

.9 1 1.1 S 

T

PER3

 

4,6 

In Remote  Alarm 

7.3 

8.1 

8.8 

T

PER4

 4,6 

Pushbutton 

Test 

  250    mS 

STROBE and IRED Pulse 
Period 

T

PER5

 4,6 

Chamber Test  or Low Battery 
Test, no Alarms 

28.8  35.2 S 

IRED On Time 

T

ON2 

6 Operating, 

Note 2

 94 

104 

115 

uS 

T

HON1 

8,9 

Operating, Alarm Condition, Note 1 

450 

500 

550 

mS 

Horn On Time 

T

HON2 

8,9 

Low Battery or Failed Chamber 
Test , No Alarm 

7.1 7.9 8.6 mS 

T

HOF1 

8,9 

Operating, Alarm Condition, Note 1 

450 

500 

550 

mS 

T

HOF2 

8,9 

Operating, Alarm Condition, Note 1 

1.35 

1.5 

1.65 

Horn Off Time 

T

HOF3 

8,9 

Low Battery or Failed Chamber 
Test, No Alarm 

28.8 32.4 35.2  S 

IO Charge Dump Duration 

T

IODMP

 7 

At Conclusion of Local Alarm or 
Test 

.68  1.1 S 

IO Delay 

T

IODLY1

 7 

From Start of Local Alarm to IO 
Active 

 0  S 

IO Filter 

T

IOFILT

 7 

IO pulse width guaranteed to be 
filtered.  IO as Input, No Local 
Alarm 

  

450 

mS 

Remote Alarm Delay 

T

IODLY2

 7 

No Local Alarm, From IO Active 
Horn Active 

.9  

1.65 

 

Note 1 - See timing diagram for Horn Temporal Pattern 
Note 2 - T

POSC

 

and T

ON2

 

are 100%

 

production tested. All other timing is guaranteed by functional testing. 

 
Typical values are for design information and are not guaranteed. 
Limits over the specified temperature range are not production tested and are based on characterization data. 

 

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RE46C141 

CMOS Photoelectric Smoke Detector ASIC with Interconnect                             

        

R&E International

 

Product Specification                                                                                                          

A Subsidiary of Microchip Technology

 

Inc.

 

 

Functional Block Diagram 

 
 

 

 
 

Figure 1

© 2009 Microchip Technology Inc.                                                                                                                  DS22177B-page 5 
       

                                                                  

 

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RE46C141 

CMOS Photoelectric Smoke Detector ASIC with Interconnect                             

        

R&E International

 

Product Specification                                                                                                          

A Subsidiary of Microchip Technology

 

Inc.

 

© 2009 Microchip Technology Inc.                                                                                                                  DS22177B-page 6 
       

                                                                  

 

 

 

PIN DESCRIPTIONS 

 

PIN# 

PIN NAME 

DESCRIPTION 

C1 

The capacitor connected to this pin sets the photo amplifier gain (high) for the 
push-to-test and chamber sensitivity test. The size of this capacitor will depend 
on the chamber background reflections. A=1+ (C1/10) where C1 is in pF. The 
gain should be <10000. 

C2 

The capacitor connected to this pin sets the photo amplifier gain (normal) during 
standby. The value of this capacitor will depend on the smoke sensitivity 
required. A=1+ (C2/10) where C2 is in pF.  

DETECT 

Positive input to the photo amplifier. This input is normally connected to the 
cathode of an external photo diode operated at zero bias.  

STROBE 

Regulated output voltage of VDD-5 which is active during a test for smoke. This 
output is the negative side of the photo amplifier circuitry. 

VDD 

Connect to the positive supply voltage 

IRED 

Provides a regulated pulsed output voltage pre-driver for the infrared emitter. 
This output usually drives the base of an NPN transistor.  

IO 

This bidirectional pin provides the capability to interconnect many detectors in a 
single system. This pin has an internal pull-down device. 

HB 

This pin is connected to the metal electrode of a piezoelectric transducer. 

HS 

HS is a complementary output to HB and connects to the ceramic electrode of 
the piezoelectric transducer.  

10 

FEED 

Usually connected to the feedback electrode through a current limiting resistor. If 
not used this pin must be connected to VDD or VSS. 

11 

LED 

Open drain NMOS output used to drive a visible LED.  

12 

COSC 

A capacitor connected to this pin with parallel resistor sets the internal clock low 
time which is approximately the clock period. 

13 

ROSC 

A resistor between this pin and pin 12 (COSC) sets the internal clock high time. 
This also sets the IRED pulse width (100-200uS). 

14 

VSS 

Connect to the negative supply voltage. 

15 

LBSET 

This input is connected to a VDD reference voltage to set the low battery 
warning voltage. 

16 

TEST 

This input is used to invoke two test modes. This input has an internal pull-down. 

 
 

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RE46C141 

CMOS Photoelectric Smoke Detector ASIC with Interconnect                             

        

R&E International

 

Product Specification                                                                                                          

A Subsidiary of Microchip Technology

 

Inc.

 

 

 

 

Typical Application 

 

 

 
 

 

Figure 2 

 

Notes:  

 
1. 

C3 should be located as close as possible to the device power pins. 

2. 

C3 is typical for an alkaline battery. This capacitance should be increased to 4.7uF or greater for a carbon battery. 

3. 

R10, R11 and C6 are typical values and may be adjusted to maximize sound pressure. 

© 2009 Microchip Technology Inc.                                                                                                                  DS22177B-page 7 
       

                                                                  

 

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RE46C141 

CMOS Photoelectric Smoke Detector ASIC with Interconnect                             

        

R&E International

 

Product Specification                                                                                                          

A Subsidiary of Microchip Technology

 

Inc.

 

© 2009 Microchip Technology Inc.                                                                                                                  DS22177B-page 8 
       

                                                                  

 

 

 

CIRCUIT DESCRIPTION AND APPLICATION NOTES 

 

Note: All timing references are nominal. See electrical characteristics for limits. 

 

Standby Internal Timing – With the external components specified in the typical application figure for ROSC and 
COSC the internal oscillator has a nominal period of 7.9mS. Normally the analog circuitry is powered down to 
minimize standby current (typically 4uA at 9V). Once every 8.1 seconds the detection circuitry (normal gain) is 
powered up for 7.9mS. Prior to completion of the 7.9mS period the IRED pulse is active for 100uS. At the 
conclusion of this 7.9mS period the photo amplifier is compared to an internal reference to determine the 
chamber status and latched. If a smoke condition is present the period to the next detection decreases and 
additional checks are made. Three consecutive smoke detections will cause the device to go into alarm and the 
horn circuit and interconnect will be active. 
Once every 32 seconds the status of the battery voltage is checked. This status is checked and latched at the 
conclusion of the LED pulse. In addition, once every 32 seconds the chamber is activated and using the high gain 
mode (capacitor C1) a check of the chamber is made by amplifying background reflections. If either the low 
battery or the photo chamber test fails the horn will chirp for 7.9mS every 32 seconds. 
The oscillator period is determined by the values of R9, R12 and C5 (see typical application FIG 2). The oscillator 
period T=T

R

+ T

F

 where T

R

 =.6931 * R12 * C5 and T

F

 =.6931 * R9 * C5 

 
Smoke Detection Circuitry – A comparator compares the photo amp output to an internal reference voltage. If the 
required number of consecutive smoke conditions is met the device will go into local alarm and the horn will be 
active. In local alarm the C2 gain is internally increased by ~10% to provide alarm hysteresis. 
 
Push to Test Operation – If the TEST input pin is activated (Vih) then, after one internal clock cycle, the smoke 
detection rate increases to once every 250mS. In this mode the high gain capacitor C1 is selected and 
background reflections are used to simulate a smoke condition. After the required consecutive detections the 
device will go into a local alarm condition. When the TEST input is deactivated (Vil) and after one clock cycle the 
normal gain capacitor C1 is selected. The detection rate continues at once every 250mS until 3 consecutive no 
smoke conditions are detected. At this point the device returns to standby timing. 
 
LED Operation – In standby the LED is pulsed on for 7.9mS every 32 Seconds. In a local alarm condition or the 
push to test alarm the LED pulse frequency is increased to once every 0.5 seconds. In the case of a remote alarm 
the LED not active. 
 
Interconnect Operation – The bidirectional IO pin allows for interconnection of multiple detectors. In a local alarm 
condition this pin is driven high immediately through a constant current source. Shorting this output to ground will 
not cause excessive current. The IO is ignored as an input during a local alarm. 
The IO pin also has an NMOS discharge device that is active for 1 second after the conclusion of any type of local 
alarm. This device helps to quickly discharge any capacitance associated with the interconnect line. 
If a remote active high signal is detected the device goes into remote alarm and the horn will be active. Internal 
protection circuitry allows for the signaling unit to have a higher supply voltage than the signaled unit without 
excessive current draw. 
The interconnect input has a 500mS nominal digital filter. This allows for interconnection to other types of alarms 
(carbon monoxide for example) that may have a pulsed interconnect signal. 

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RE46C141 

CMOS Photoelectric Smoke Detector ASIC with Interconnect                             

        

R&E International

 

Product Specification                                                                                                          

A Subsidiary of Microchip Technology

 

Inc.

 

© 2009 Microchip Technology Inc.                                                                                                                  DS22177B-page 9 
       

                                                                  

 

 
Low Battery and Chamber Test – In standby an internal reference is compared to the voltage divided VDD supply. 
Low battery status is latched at the conclusion of the LED pulse. The horn will chirp for 7.9ms every 32 seconds 
until the low battery condition no longer exists. In standby a chamber test is also performed every 32 seconds by 
switching to the high gain capacitor C1 and sensing the photo chamber background reflections. Two consecutive 
chamber tests failures will also cause the horn to chirp for 7.9mS every 32 seconds. The low battery chirp occurs 
next to the LED pulse and the failed chamber test chirp 16.2 seconds later. The low battery and chamber tests 
are not performed in a local or remote alarm condition. The low battery alarm threshold is approximately equal to 
((5*R15)/R14)+5 where R15 and R16 are in the same units.  
 
Diagnostic Mode – In addition to the normal function of the TEST input a special diagnostic mode is available for 
calibration and test of the smoke detector. Taking the TEST pin below VSS and sourcing ~300uA out of the pin 
for 1 clock cycle will enable the diagnostic mode. In the diagnostic mode some of the pin functions are redefined. 
Refer to the table below for redefined pin functions in the diagnostic mode. In addition in this mode STROBE is 
always enabled and the IRED is pulsed at the clock rate of 10.5mS nominal. 
 
 
Pin Name  Pin Number 

Description 

IO 

Disabled as an output. A high on this pin directs the photo amplifier output to pin C1 
(1) or C2 (2), determined by the level on LBSET (15). Amplification occurs during 
the IRED active time. 

LBSET 

15 

If IO is high then this pin controls the gain capacitor that is used. If LBSET is low 
then normal gain is selected and the photo amp output appears on C1 (1). If LBSET 
is high then high gain is selected and the photo amp output is on C2 (2). 

FEED 

10 

If LBSET (15) is low then taking this input high will enable hysteresis, which is a 
nominal 10% gain increase in normal gain mode. 

COSC 

12 

If desired this pin can be driven by an external clock. 

HORNB 

This pin becomes the smoke integrator output.  A high level indicates that an alarm 
condition has been detected. 

LED 

11 

The LED pin is used as a low battery indicator. For VDD above the low battery 
threshold the open drain NMOS is off. If VDD falls below the threshold the NMOS 
turns on. 

 
 
 

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RE46C141 

CMOS Photoelectric Smoke Detector ASIC with Interconnect                             

        

R&E International

 

Product Specification                                                                                                          

A Subsidiary of Microchip Technology

 

Inc.

 

 

Timing Diagrams 

 

Standby Timing, No Alarm (not to scale)

Oscillator

T

POSC

T

PWOSC

Internal Clock

T

ON1

T

PER1

STROBE

T

ON2

IRED

T

PLED1

LED

Low Supply or Chamber Test Failure

LED

Low BatteryTest

T

HON3

Low BatteryWarning Chirp

Low Battery Warning Chirp

Horn

T

HOF3

Chamber Test and Warning is Offset from Low Battery Test and Warning by 21.5 Seconds

 

© 2009 Microchip Technology Inc.                                                                                                                  DS22177B-page 10 
       

                                                                  

 

Maker
Microchip Technology Inc.
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