RE46C129
CMOS Ionization Smoke Detector ASIC with Interconnect
Product Specification
R&E International
DEVICE DESCRIPTION and APPLICATION NOTES
Internal Timing – With external components as indicated on the application drawing the period of the
oscillator is nominally 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. In any alarm condition the
horn is on for 166mS and off for 83mS (typical).
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 must be provided externally on pin 13
(VSEN). See the application drawing (FIG 2).
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 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 10.5mS LED pulse. Pin 3 (LBADJ) can be used to modify the low battery set point by
placing a resistor to VDD or VSS. The transmission switch on LBADJ is turned on during the LED pulse
so an external resistance can be added on pin 3 to modify the set point if desired.
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.
Interconnect – Pin 2 (IO) provides the capability to common many detectors in a single system. If a single
unit goes into alarm the IO pin is driven high. This high signal causes the interconnected units to alarm.
The LED flashes every 1S for 10.5mS on the signaling unit and is inhibited on the units that are in alarm
due to the active IO signal. An internal sink device on the IO pin helps to discharge the interconnect line.
This charge dump device is active for 1 clock cycle after the unit exits a local alarm condition (1.67S).
The interconnect input has a 500mS nominal digital filter which will filter out pulsed signals on the IO pin.
This allows for interconnection to other types of alarms (carbon monoxide for example) that may have a
pulsed interconnect signal. This filter will eliminate unwanted random horn activations caused by a pulsed
(<500ms nominal) IO input signal.
Testing - By holding pin 12 (OSCAP) low the internal power strobe is active. Functional testing can be
accelerated by driving pin 12 with a 4kHZ square wave however the 10.5mS strobe period must be
maintained for proper operation of the analog circuitry. Please refer to the timing diagrams. All internal
timing is reset after a power up. By holding pins 8 and 12 low, reducing VDD and monitoring Pin 10 the
low battery trip level can be measured at power up.
Telephone 610.992.0727
Page 5 of 8
E-mail: rande@randeint.com
DS-RE46C129-121806
This datasheet contains PROPRIETARY and CONFIDENTIAL information.
Facsimile 610.992.0734
RANDE [ R & E INTERNATIONAL, INC. ]
