RE46C120 データシートの表示（PDF） - R and E International, Inc.

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RE46C120

CMOS Ionization Smoke Detector ASIC

R and E International, Inc. 

RE46C120

CMOS Ionization Smoke Detector ASIC

Product Specification

R&E International

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 4kHZ 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).

Telephone 610.992.0727

Facsimile 610.992.0734

E-mail: rande@randeint.com

Page 4 of 7

DS-RE46C120-010907

This datasheet contains PROPRIETARY and CONFIDENTIAL information.

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