R&E International
A Subsidiary of Microchip Technology Inc.
RE46C120
CMOS Ionization Smoke Detector ASIC
Product Specification
General Description
The RE46C120 is a low power CMOS ionization type
smoke detector IC. With a few external components
this circuit will provide all the required features for an
ionization type smoke detector.
An internal oscillator strobes power to the smoke
detection circuitry for 10.5mS every 1.66 seconds to
keep standby current to a minimum. A check for a low
battery condition is performed every 40 seconds when
in standby. The TONE input allows for selection of a
temporal pattern or a 2/3 duty cycle continuous tone.
The temporal horn pattern supports the NFPA 72
emergency evacuation signal.
Although this device was designed for smoke detection
utilizing an ionization chamber it could be used in a
variety of security applications.
Utilizing low power CMOS technology the RE46C120
was designed for use in smoke detectors that comply
with Underwriters Laboratory Specification UL217 and
UL268.
Features
•
•
•
•
•
•
•
•
•
•
Guard Outputs for Ion Detector Input
+/-0.75pA Detect Input Current
Internal Reverse Battery Protection
Internal Low Battery Detection
Pin Selectable Horn Pattern
Low Quiescent Current Consumption (<6.5uA)
16L PDIP
ESD Protection on all Pins
Compatible with MC145017, MC14467
Available in RoHS Compliant Pb Free Packaging
Pin Configuration
DETCOMP
N/C
LBADJ
TONE
LED
VDD
RBIAS
FEED
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
GUARD2
DETECT
GUARD1
VSEN
OSCAP
HS
HB
VSS
ABSOLUTE MAXIMUM RATINGS
PARAMETER
Supply Voltage
Input Voltage Range Except FEED
FEED Input Voltage Range
Reverse Battery Time
Input Current except FEED
Operating Temperature
Storage Temperature
Maximum Junction Temperature
SYMBOL
V
DD
V
in
V
infd
T
RB
I
in
T
A
T
STG
T
J
VALUE
15
-.3 to V
dd
+.3
-10 to +22
5
10
-10 to 60
-55 to 125
150
UNITS
V
V
V
S
MA
°C
°C
°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
© 2009 Microchip Technology Inc.
DS22157A-page 1
RE46C120
CMOS Ionization Smoke Detector ASIC
Product Specification
R&E International
A Subsidiary of Microchip Technology Inc.
DC Electrical Characteristics at TA = 25°C, VDD=9V, VSS=0V (unless otherwise noted)
Test
Pin
6
6
6
4,8
4,8
15
15
4
8
15
15
8
5
10,11
1
10,11
1
5
6
13
3
14,15
15,16
13,15
14,15
13,15
14,16
13
Guard Amplifier
Guard Amplifier
Smoke Comparator
Guard Amplifier, Note 2
Smoke Comparator, Note 2
Guard Amplifier Outputs, Note 2
No Alarm to Alarm Condition
VDD=9V, DETECT=VSS, 0-40% RH
VDD=9V, DETECT=VSS, 85% RH
Note 1
TONE=VSS, RBIAS=8.2MΩ,
FEED=-10V
VDD=9V, DETECT=VDD, 0-40% RH
VDD=9V, DETECT=VDD, 85% RH
Note 1
FEED=22V
LED Off
IOH=-16mA, VDD=7.2V
IOH=-30ua
IOL=16mA, VDD=7.2V
IOL=30ua
IOL=10mA, VDD=7.2V
T
A
=-10 to 60ºC, Note 3
Parameter
Supply Voltage
Supply Current
Symbol
V
DD
I
DD1
I
DD2
V
IH
V
IL
IL
DET1
IL
DET2
IL
TONE
IL
FD
Test Conditions
Operating
RBIAS=8.2MΩ, OSCAP=.1uF
RBIAS=8.2MΩ, OSCAP=.1uF;Vdd=12V
Min
6
Limits
Typ
Max
12
4.5
6.5
9
Units
V
uA
uA
V
V
pA
pA
nA
uA
pA
pA
uA
uA
V
V
Input Voltage High
Input Voltage Low
Input Leakage Low
6.2
4.5
4.5
2.7
-0.75
-1.50
-100
-450
-50
0.75
1.50
50
1
Input Leakage High
IH
DET1
IH
DET2
IH
FD
Output Off Leakage High
Output Voltage High
I
OHZ
V
OH1
V
OH2
V
OL1
V
OL2
V
OL3
6.3
8.5
.9
.5
3
7.2
47
-50
-50
-50
2
.5
10
90
130
170
7.5
50
65.5
50
50
50
V
DD
-.5
V
DD
-2
7.8
53
Output Voltage Low
V
V
V
V
%V
DD
%V
DD
mV
mV
mV
V
V
kΩ
mV
Low Battery Voltage
Internal Sensitivity Set Voltage
V
LB
V
SET1
V
SET2
VG
OS1
VG
OS2
VG
OS3
Offset Voltage
Common Mode Voltage
V
CM1
V
CM2
Z
OUT
V
HYS
Output Impedance
Hysteresis
Note 1: Sample test only
Note 2: Not 100% production tested
Note 3: Production test at room with temperature guardbanded limits.
© 2009 Microchip Technology Inc.
DS22157A-page 2
RE46C120
CMOS Ionization Smoke Detector ASIC
Product Specification
R&E International
A Subsidiary of Microchip Technology Inc.
AC Electrical Characteristics at TA = 25°C, VDD=9V, OSCAP=.1uF, RBIAS=8.2MΩ, VSS=0V (unless
otherwise noted)
Test
Pin
12
12
5
5
5
5
10,11
10,11
10,11
10,11
10,11
10,11
10,11
Parameter
Oscillator Period
Symbol
T
PER1
T
PER2
T
PW
T
LON
T
LOF1
T
LOF2
T
HON1
T
HON2
T
HON3
Test Conditions
No Alarm Condition
Alarm Condition
Operating
Operating
Standby, No Alarm
Alarm Condition
Operating, Alarm Condition, Note 4,
TONE=VDD or Float
Low Battery, No Alarm
Operating, Alarm Condition, TONE=Low
Operating, Alarm Condition, Note 4,
TONE=VDD or Float
Operating, Alarm Condition, Note 4,
TONE=VDD or Float
Operating, Alarm Condition, TONE=Low
Low Battery, No Alarm
Min
1.34
37.5
9.1
9.1
32
.9
450
9.1
150
450
1.35
75
32
Limits
Typ
Max
1.67
41.5
10.5
10.5
40
1
500
10.5
166
500
1.5
83
40
2
45.8
12.9
12.9
48
1.1
550
12.9
183
550
1.65
92
48
Units
S
mS
mS
mS
S
S
mS
mS
mS
mS
S
mS
S
Oscillator Pulse Width
LED On Time
LED Off Time
Horn On Time
Horn Off Time
T
HOF1
T
HOF2
T
HOF3
T
HOF4
Note 4: See timing diagram for Horn Temporal Pattern
Functional Block Diagram
Figure 1
© 2009 Microchip Technology Inc.
DS22157A-page 3
RE46C120
CMOS Ionization Smoke Detector ASIC
Product Specification
R&E International
A Subsidiary of Microchip Technology Inc.
DEVICE DESCRIPTION and APPLICATION NOTES
Note: All timing references are nominal values. Refer to the electrical specifications for limits
Internal Timing – With external components as indicated on the application drawing the period of the oscillator is
1.67 seconds in standby. Every 1.66 seconds the detection circuitry is powered up for 10.5mS and the status of
the smoke comparator is latched. In addition every 40 seconds the LED driver is turned on for 10.5mS and the
status of the low battery comparator is latched. The smoke comparator status is not checked during the low
battery test, during the low battery horn warning chirp, or when the horn is on due to an alarm condition.
If an alarm condition is detected the oscillator period increases to 41.5mS.
Due to the low currents used in the oscillator the capacitor on pin 12 should be a low leakage type. Oscillator
accuracy will depend mainly on the tolerance of the RBIAS resistor and OSCAP capacitor.
Smoke Detection Circuit – The smoke comparator compares the ionization chamber voltage to a voltage derived
from a resistor divider across VDD. This divider voltage is available externally on pin 13 (VSEN). When smoke is
detected this voltage is internally increased by 130mV nominal to provide hysteresis and make the detector less
sensitive to false triggering.
Pin 13 (VSEN) can be used to modify the internal set point for the smoke comparator by using external resistors
to VDD or VSS. Nominal values for the internal resistor divider are indicated on the block diagram. These internal
resistor values can vary by up to ±20% but the resistor matching will typically be <2% on any one device. A
transmission switch on pin 13 isolates this pin during the low battery test so that the low battery set point will not
be affected if external resistors are used to modify the smoke sensitivity set point.
The guard amplifier and outputs are always active and will be within 50mV of the DETECT input to reduce surface
leakage. The guard outputs also allow for measurement of the DETECT input without loading the ionization
chamber.
Low Battery Detection – An internal Zener reference is compared to the voltage divided VDD supply. The battery
can be checked under load via the LED low side driver output since low battery status is latched at the end of the
10mS LED pulse. Pin 3 (LBADJ) can be used to modify the low battery set point by placing a resistor to VDD or
VSS. Note that the internal resistor string is common to both pin 3 and pin 13 so there will be some interaction
between the two. Modification of the low battery set point may affect the smoke sensitivity setting.
LED Pulse – The LED is pulsed on for 10.5mS every 40S in standby. In alarm the LED is pulsed on for 10.5mS
every 1S.
Testing – At power up all internal registers are reset. By holding pin 12 (OSCAP) low the internal power strobe is
active. Functional testing can be accelerated by driving pin 12 with a 4 kHz square wave however the 10.5mS
strobe period should be maintained for proper operation of the analog circuitry. Please refer to the timing
diagrams.
Horn Tone – Pin 4 selects the NFPA72 horn tone (high or floating) or the 2/3 duty cycle continuous tone (low). If
this pin is externally connected high, use a current limiting resistor from pin 4 to VDD.
Reverse Battery Protection – The RE46c120 internally limits the current from VSS to VDD in the event of
accidental polarity reversal. If an input is connected to VDD it should be done through a resistance of at least
1.5K to limit the reverse current through this path.
© 2009 Microchip Technology Inc.
DS22157A-page 4
RE46C120
CMOS Ionization Smoke Detector ASIC
Product Specification
R&E International
A Subsidiary of Microchip Technology Inc.
Typical Application
Figure 2
Notes:
1.
2.
3.
4.
Float or connect pin 4 to VDD through 1.5kOhm minimum for NFPA72 temporal horn pattern, connect to VSS for 2/3 duty cycle
continuous tone.
R3, R4 and C1 are typical values and may be adjusted to maximize sound pressure.
C2 should be located as close as possible to the device power pins.
Route the pin 8 PC board trace away from pin 7 to avoid coupling.
© 2009 Microchip Technology Inc.
DS22157A-page 5
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