2009-2012 Microchip Technology Inc.
DS22181C-page 1
RE46C145
Features:
• Internal Power On Reset
• Low Quiescent Current Consumption
• ESD Protection on all Pins
• Interconnect up to 40 Detectors
• 10 Minute Timer for Sensitivity Control
• Temporal Horn Pattern
• Internal Low Battery and Chamber Test
• Compatible with Allegro A5366
• Alternate Diagnostic Mode
• UL Recognized per File S24036
General Description:
The RE46C145 is a low-power, CMOS photoelec-
tric-type smoke detector IC. With minimal external
components, this circuit will provide all the required fea-
tures 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 100 µs every 10 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.
In diagnostic mode, the photo amplifier output is avail-
able on pin 15 for production calibration of the photo
chamber.
When in Standby, a check for a low battery condition
and chamber integrity is performed every 43 seconds.
The temporal horn pattern supports the NFPA 72
emergency evacuation signal.
An interconnect pin allows multiple detectors to be con-
nected such that when one units alarms, all units will
sound.
An internal 10 minute timer can be used for a reduced
sensitivity mode.
The RE46C145 is recognized by Underwriters
Laboratories for use in smoke detectors that comply
with specification UL217 and UL268.
Package Types
RE46C145
PDIP, SOIC, SOICN
C1
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
C2
DETECT
STROBE
V
DD
IRED
IO
HORNB
TEST
VSEN
V
SS
ROSC
COSC
LED
FEED
HORNS
CMOS Photoelectric Smoke Detector ASIC with Interconnect
and Timer Mode
RE46C145
DS22181C-page 2
2009-2012 Microchip Technology Inc.
Functional Block Diagram
Typical Application
Logic and
Timing
Bias and
Power Reset
Oscillator
+
-
+
-
VDD (5)
VSEN (15)
C1 (1)
DETECT (3)
C2 (2)
TEST (16)
IO (7)
FEED (10)
HS (9)
LED (11)
IRED (6)
ROSC (13)
COSC (12)
HB (8)
+
-
PHOTOAMP
STROBE (4)
VSS (14)
V
DD
-3.5V
V
DD
-5V
Low Battery
Smoke Comparator
Horn Driver
Push-to-Test
C3
1 μF
C5
1.5nF
R12
10M
R9
100k
R13
330
D3
C6
1.0nF
R10
1.5M
R11
220k
R8
100
R7
22
C4
100 μF
D5
D6
R4
560
C2
4700 pF
C1
.047 μF
R1
4.7k
R2
5k
R3
8.2k
R
ADJ2
R
ADJ1
R6
1k
1
2
3
4
5
14
6
7
8
9
10
11
12
13
15
16
R5
250k
To Other Units
Q3
9V
Battery
Smoke Chamber
Note 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 4.7 µF or greater for a carbon battery.
3:
R10, R11 and C6 are typical values and may be adjusted to maximize sound pressure.
2009-2012 Microchip Technology Inc.
DS22181C-page 3
RE46C145
1.0
ELECTRICAL
CHARACTERISTICS
1.1
Absolute Maximum Ratings†
V
DD
....................................................................................15V
Input Voltage Range Except FEED, IO .......... V
IN
= -.3V to V
DD
+.3V
FEED Input Voltage Range ..................... V
INFD
=-10 to +22V
IO Input Voltage Range................................. V
IO1
= -.3 to 15V
Input Current except FEED................................... I
IN
= 10 mA
Operating Temperature ................................T
A =
-25 to +75°C
Storage Temperature ............................T
STG
= -55 to +125°C
Maximum Junction Temperature......................... T
J
= +150°C
† Notice:
Stresses above those listed under “Maximum
ratings” may cause permanent damage to the device.
This is a stress rating only and functional operation of
the device at these or any other conditions above those
indicated in the operation listings of this specification is
not implied. Exposure to maximum rating conditions for
extended periods may affect device reliability.
DC ELECTRICAL CHARACTERISTICS
DC Electrical Characteristics:
Unless otherwise indicated, all parameters apply at T
A
= -25°C to +75°C, V
DD
= 9V
Parameter
Symbol
Test
Pin
Min
Typ
Max
Units
Conditions
Supply Voltage
V
DD
5
6
—
12
V
Operating
Supply Current
I
DD1
5
—
4
6
µA
Configured as in
Typical
Application
, COSC = V
SS
,
LED off
I
DD2
5
—
5.5
8
µA
Configured as in
Typical
Application
, V
DD
= 12V,
COSC = V
SS
I
DD3
5
—
—
2
mA
Configured as in
Typical
Application
, STROBE on,
IRED off, V
DD
=12V
I
DD4
5
—
—
3
mA
Configured as in
Typical
Application
, STROBE on,
IRED on, V
DD
= 12V,
Note 1
Input Voltage High
V
IH1
10
6.2
—
—
V
FEED
V
IH2
7
3.2
—
—
V
No Local Alarm, IO as Input
V
IH3
15
1.6
—
—
V
V
SEN
V
IH4
16
8.5
—
—
V
TEST
Input Voltage Low
V
IL1
10
—
—
2.7
V
FEED
V
IL2
7
—
—
1.5
V
No Local Alarm, IO as Input
V
IL3
15
—
—
.5
V
V
SEN
V
IL4
16
—
—
7 V
TEST
Input Leakage Low
I
IL1
1,2,3
—
—
-100
nA
V
DD
= 12V, COSC = 12V,
STROBE active
I
IL2
10,12
—
—
-100
nA
V
DD
= 12V, V
IN
= V
SS
I
IL3
15,16
—
—
-1
µA
V
DD
= 12V, V
IN
= V
SS
I
LFD
10
—
—
-50
µA
FEED = -10V
Note 1:
Does not include Q3 emitter current.
2:
Not production tested.
3:
Typical values are for design information and are not ensured.
4:
Limits over the specified temperature range are not production tested and are based on characterization
data.
RE46C145
DS22181C-page 4
2009-2012 Microchip Technology Inc.
Input Leakage High
I
IH1
1,2
—
—
100
nA
V
DD
= 12V, V
IN
= V
DD
,
STROBE active
I
IH2
3,10,12
—
—
100
nA
V
DD
= 12V, V
IN
= V
DD
I
HFD
10
—
—
50
µA
FEED = 22V
Input Pull Down Current
I
PD1
16
.25
—
10
µA
V
IN
= V
DD
I
PD2
15
.1
.25
.5
µA
V
IN
= V
DD
I
PDIO1
7
20
—
80
µA
V
IN
= V
DD
I
PDIO2
7
—
—
140
µA
V
IN
= 15V, V
DD
= 12
Output Leakage
Current Low
I
OZL1
11,13
—
—
-1
µA
Output Off, Output = V
SS
Output Leakage
Current High
I
OZH1
11,13
—
—
1
µA
Output Off, Output = V
DD
Output Voltage Low
V
OL1
8,9
—
—
1
V
Iol = 16 mA, V
DD
= 6.5V
V
OL2
13
—
.5
—
V
Iol = 5 mA, V
DD
= 6.5V
V
OL3
11
—
—
.6
V
Iol = 10 mA, V
DD
= 6.5V
Output Voltage High
V
OH1
8,9
5.5
—
V
Iol = -16 mA, V
DD
= 6.5V
Output Current
I
IOH1
7
-4
—
-16
mA
Alarm, V
IO
= V
DD
–2V or
V
IO
= 0V
I
IODMP
7
5
—
—
mA
At Conclusion of Local Alarm
or Test, VV
IO
= 1V
Low Battery
Alarm Voltage
V
LB
5
6.9
7.2
7.5
V
Output Voltage
V
STOF
4
V
DD
–.1
—
—
V
STROBE off, V
DD
= 12V,
I
OUT
= -1 µA
V
STON
4
V
DD
–
5.25
V
DD
–5 V
DD
–4.75
V
STROBE on, V
DD
= 9V
I
OUT
= 100 µA to 500 µA
V
IREDOF
6
—
—
.1
V
IRED off, V
DD
= 12V,
I
OUT
= 1 µA
V
IREDON
6
2.85
3.1
3.35
V
IRED on, V
DD
= 9V
I
OUT
= 0 to -6 mA, T
A
= +25°C
Common Mode Voltage
V
CM1
1,2,3
.5
—
V
DD
–2
V
Local smoke,
Push to Test or Chamber Test,
Note 2
Smoke Comparator
Reference
V
REF
-
V
DD
–3.7
—
V
DD
–3.3
V
Internal Reference
Temperature Coefficient
T
CST
4
—
.01
—
%/ºC V
DD
= 6V to 12V,
STROBE Output Voltage
T
CIRED
6
—
.3
—
%/ºC V
DD
= 6V to 12V,
IRED Output Voltage
Line Regulation
V
STON
4,5
—
-50
—
dB
Active, V
DD
=6V to 12V
V
IREDON
6,5
—
-30
—
dB
Active, V
DD
= 6V to 12V
DC ELECTRICAL CHARACTERISTICS (CONTINUED)
DC Electrical Characteristics:
Unless otherwise indicated, all parameters apply at T
A
= -25°C to +75°C, V
DD
= 9V
Parameter
Symbol
Test
Pin
Min
Typ
Max
Units
Conditions
Note 1:
Does not include Q3 emitter current.
2:
Not production tested.
3:
Typical values are for design information and are not ensured.
4:
Limits over the specified temperature range are not production tested and are based on characterization
data.
2009-2012 Microchip Technology Inc.
DS22181C-page 5
RE46C145
AC ELECTRICAL CHARACTERISTICS
AC Electrical Characteristics:
Unless otherwise indicated, all parameters apply at T
A
= -25°C to +75°C, V
DD
= 9V,
V
SS
= 0V, Component Values from
Typical Application
; R
9
= 100 K
, R
12
= 10 M
, C
5
= 1.5 nF
Parameter
Symbol
Test
Pin
Min
Typ
Max
Units
Test Conditions
Oscillator Period
T
POSC
12
9.4
10.5
11.5
ms
No alarm condition
LED and STROBE
On Time
T
ON1
11,4
9.4
10.5
11.5
ms
Operating
LED Period
T
PLED1
11
39
43
47
s
Standby, no alarm
T
PLED2
11
.45
.5
.55
s
Local alarm condition
T
PLED3
11
9.6
10.75
11.8
s
Timer mode, no local alarm
T
PLED4
11
LED IS NOT ON
s
Remote alarm only
STROBE
and IRED Pulse
Period
T
PER1
4,6
9.6
10.75
11.8
s
Standby, no alarm
T
PER1A
4,6
1.8
2
2.2
s
Standby, after one valid smoke
sample
T
PER1B
4,6
.9
1
1.1
s
Standby, after two consecutive
valid smoke samples
T
PER2
4,6
.9
1
1.1
s
In Local Alarm (three consecu-
tive valid smoke samples)
T
PER3
4,6
7.2
8
8.9
s
In Remote Alarm
T
PER4
4,6
300
336
370
ms
Push-button test
T
PER5
4,6
39
47
s
Chamber Test or Low Battery
Test, no alarms
IRED On Time
T
ON2
6
94
104
115
µs
Operating
Horn On Time
T
HON1
8,9
450
500
550
ms
Operating, alarm condition,
Note 1
T
HON2
8,9
9.5
10.5
11.5
ms
Low Battery or Failed Chamber
test , no alarm
Horn Off Time
T
HOF1
8,9
450
500
550
ms
Operating, alarm condition,
Note 1
T
HOF2
8,9
1.35
1.5
1.65
s
Operating, alarm condition,
Note 1
T
HOF3
8,9
39
43
47
s
Low Battery or Failed Chamber
test, no alarm
IO Charge
Dump Duration
T
IODMP
7
.9
1.46
s
At the conclusion of the Local
Alarm or Test
IO Delay
T
IODLY1
7
0
s
From start of Local Alarm to
IO Active
IO Filter
T
IOFILT
7
600
mSs
IO pulse-width ensured to be
filtered. IO as input, no local
alarm
Remote
Alarm Delay
T
IODLY2
7
1.05
2.0
s
No local alarm, from IO Active
to Horn Active
Timer Period
T
TPER
7
8.5
10
Min
No alarm condition,
Note 2
Note 1:
See timing diagram for Horn Temporal Pattern
2:
During the Timer mode, the LED period is 10.5 seconds. The LED period will return to 43 seconds at the
conclusion of the Timer mode.
3:
T
POSC
and T
ON2
are 100% production tested. All other timing is ensured by functional testing.
4:
Typical values are for design information and are not ensured.
RE46C145
DS22181C-page 6
2009-2012 Microchip Technology Inc.
TEMPERATURE CHARACTERISTICS
Electrical Specifications:
Unless otherwise indicated, V
DD
= 9V, V
SS
= 0V
Parameters
Sym.
Min.
Typ.
Max.
Units
Conditions
Temperature Ranges
Operating Temperature Range
T
A
-25
—
+75
°C
Storage Temperature Range
T
STG
-55
—
+125
°C
Thermal Package Resistances
Thermal Resistance, 16L-PDIP
θJ
A
—
70
—
°C/W
Thermal Resistance, 16L-SOIC (150 mil.)
θJ
A
—
86.1
—
°C/W
Thermal Resistance, 16L-SOIC (300 mil.)
θJ
A
—
80
—
°C/W
2009-2012 Microchip Technology Inc.
DS22181C-page 7
RE46C145
2.0
PIN DESCRIPTION
The descriptions of the pins are listed in .
2.1
High/Normal Gain Capacitor Pins
(C1, C2)
The capacitor connected to C1 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 expressed
in pF. The gain should be
<10000.
The capacitor connected to C2 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 expressed
in pF.
2.2
Photo Diode Input (DETECT)
This input is normally connected to the cathode of an
external photo diode operated at zero bias.
2.3
Strobed Detection
Negative Supply (STROBE)
Regulated output voltage of V
DD
-5 which is active
during a test for smoke. This output is the negative side
of the photo amplifier reference circuitry.
2.4
Positive Power Supply (V
DD
)
The V
DD
pin is the device’s positive power supply input.
2.5
Infrared Emitting Diode Pin (IRED)
Provides a regulated pulsed output voltage pre-driver
for the infrared emitter. This output usually drives the
base of an NPN transistor.
2.6
Interconnect Pin (IO)
This bidirectional pin provides the capability to
interconnect many detectors in a single system. This
pin has an internal pull-down device.
2.7
Horn Brass, Inverted Output (HB)
HB pin is connected to the metal electrode of a
piezoelectric transducer.
2.8
Horn Silver Output Pin (HS)
HS pin is a complementary output to HB and connects
to the ceramic electrode of the piezoelectric transducer.
TABLE 2-1:
PIN FUNCTION TABLE
RE46C145
PDIP, SOIC, SOICN
Symbol
Function
1
C1
High Gain Capacitor Pin
2
C2
Normal Gain Capacitor Pin
3
DETECT
Photo Diode Input
4
STROBE
Strobed Detection Negative Supply
5
V
DD
Positive Power Supply
6
IRED
Infrared Emitting Diode Pin
7
IO
Interconnect Pin
8
HB
Horn Brass, Inverted Output
9
HS
Horn Silver Output
10
FEED
Horn Feedback Pin
11
LED
LED Driver Pin
12
COSC
Oscillator Capacitor Input
13
ROSC
Oscillator Resistor Drive Low
14
V
SS
Negative Power Supply
15
VSEN
HushTimer Sensitivity Pin
16
TEST
Test Pin
RE46C145
DS22181C-page 8
2009-2012 Microchip Technology Inc.
2.9
Horn Feedback Pin (FEED)
Usually this pin is connected to the feedback electrode
through a current limiting resistor. If not used, this pin
must be connected to V
DD
or V
SS
.
2.10
LED Driver Pin (LED)
This pin is an open drain NMOS output used to drive a
visible LED.
2.11
Oscillator Capacitor Input (COSC)
A capacitor connected to this pin, with a parallel
resistor, sets the internal clock low time, which is
approximately the clock period.
2.12
Oscillator Resistor Drive Low
(ROSC)
A resistor between this pin and COSC pin sets the
internal clock high time. This also sets the IRED pulse
width (100 - 200 µs).
2.13
Hush Timer Sensitivity Pin (VSEN)
In Timer mode, this input pin can be used to set an
external smoke comparator reference.
2.14
TEST Pin
This input is used to invoke two test modes and the
Timer mode. This input has an internal pull-down.
2009-2012 Microchip Technology Inc.
DS22181C-page 9
RE46C145
3.0
DEVICE DESCRIPTION
3.1
Standby Internal Timing
With the external components specified in the
Typical
Application
for R12 and C5, the internal oscillator has a
nominal period of 10 ms. Normally the analog circuitry
is powered down to minimize standby current (typically
4 µA at 9V). Once every 10 seconds the detection
circuitry (normal gain) is powered up for 10 ms. Prior to
completion of the 10 ms period, the IRED pulse is
active for 100 µs. At the conclusion of the 10 ms 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 43 seconds the status of the battery volt-
age is checked. This status is checked and latched at
the conclusion of the LED pulse. In addition, once
every 43 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 10 ms every 43 seconds.
The oscillator period is determined by the values of R9,
R12 and C5 (see
Typical Application
). The oscillator
period is as follows:
EQUATION 3-1:
3.2
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
approximately 10% to provide alarm hysteresis.
3.3
Push-to-Test Operation
If the TEST input pin is activated (V
IH
), after one
internal clock cycle, the smoke detection rate increases
to once every 330 ms. 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 (V
IL
) and after one clock cycle, the normal
gain capacitor C1 is selected. The detection rate
continues at once every 330 ms until three consecutive
no smoke conditions are detected. At this point, the
device returns to standby timing.
3.4
LED Operation
In standby, the LED is pulsed on for 10 ms every
43 seconds. In a local alarm condition or the push-to-
test alarm, the LED pulse frequency is increased to
once every .5 seconds. In the case of a remote alarm,
the LED is not active. In the Timer mode of operation,
the LED is pulsed on for 10 ms every 10 seconds.
3.5
Interconnect Operation
The bidirectional I/O 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 I/O is ignored as an input during
a local alarm.
The I/O 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 670 ms nominal digital
filter. This allows for interconnection to other types of
alarms (carbon monoxide, for example) that may have
a pulsed interconnect signal.
Note:
All timing references are nominal. See
Electrical Characteristics
for limits.
T = T
R
+ T
F
Where:
T
R
= .6931 x R12 x C5
T
F
= .6931 x R9 x C5
RE46C145
DS22181C-page 10
2009-2012 Microchip Technology Inc.
3.6
Low Battery Detection
In standby, an internal reference is compared to the
voltage divided V
DD
supply. A low battery status is
latched at the conclusion of the LED pulse. The horn
will chirp for 10 ms every 43 seconds, until the low
battery condition no longer exists. The low battery test
is not performed in a local or remote alarm condition.
The low battery notification does not sound in a local or
remote alarm condition.
3.7
Chamber Fail Detection
In standby, a chamber test is also performed every
43 seconds, by switching to the high gain capacitor C1
and sensing the photo chamber background
reflections. Two consecutive chamber test failures will
also cause the horn to chirp for 10 ms every
43 seconds. The low battery chirp occurs just before
the LED pulse (see
Figure 3-1
). The chamber test and
chamber test failure chirp occurs approximately
21 seconds after the LED pulse. The chamber tests are
not performed in a local or remote alarm condition.
The chamber fail notification does not sound in a local
or remote alarm condition.
3.8
Timer Mode
If resistors R
ADJ1
and R
ADJ2
are in place and a high-to-
low transition occurs on the TEST input, the device
enters a 10 minute timer mode. In this mode, the
smoke comparator reference is switched from the
internal V
DD
- 3.5V reference to the voltage that
appears on VSEN (pin 15). This allows the sensitivity to
be modified for the duration of the 9 minute timer
period. The chamber test is performed in Timer mode.
If VSEN is left unconnected or tied to V
SS
, the Timer
mode of operation is inhibited.
3.9
Diagnostic Mode
In addition to the normal function of the TEST input, a
special diagnostic mode is available to calibrate and
test of the smoke detector. Taking the TEST pin below
V
SS
and sourcing ~200 µA 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
Table 3-1
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 ms nominal.
TABLE 3-1:
DIAGNOSTIC MODE PIN FUNCTION
Pin Name
Pin
Number
Function
IO
7
The IO pin (7) controls the gain capacitor used for the photo amplifier. If IO is low, then
normal gain is selected. If IO is high, then high gain is selected.
VSEN
15
In Diagnostic mode, the output of the photo amplifier is gated to this pin and the pull-
down device is disabled. .
FEED
10
If the IO pin (7) 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
8
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 V
DD
above the low battery thresh-
old, the open drain NMOS is off. If V
DD
falls below the threshold, the NMOS turns on.