5347

SMOKE DETECTOR

with INTERCONNECT

and TIMER

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

Limits

Characteristic

Pin

Test Conditions

Min.

Typ.

Max.

Units

ELECTRICAL CHARACTERISTICS continued

Timer Out Output Current

4

V

OUT

= 0.5 V

500

—

—

µA

LED Output ON Current

5

V

DD

= 7.2 V, V

OUT

= 1.0 V

10

—

—

mA

LED Output ON Time

5

8.0

10

12

ms

LED Output OFF Time

5

No Alarm, In Standby

32

40

48

s

No Alarm, Timer Mode After Pin 1

High-to-Low

8.0

10

12

s

I/O Current

2

No Alarm, V

I/O

= V

DD

- 2.0 V

25

—

60

µA

Alarm, V

I/O

= V

DD

- 2.0 V

-7.5

—

—

mA

I/O Alarm Voltage

2

External “Alarm” In

3.0

—

—

V

I/O Delay

2

“Alarm” Out

—

3.0

—

s

Supply Current

6

V

DD

= 9.0 V, No Alarm, No Loads

—

5.0

9.0

µA

V

DD

= 12 V, No Alarm, No Loads

—

—

12

µA

NOTE 1: Negative current is defined as coming out of (sourcing) the specified device pin.

NOTE 2: Alarm (Smoke) Condition is defined as V

15

< V

13

; No Alarm (No Smoke) Condition as V

15

> V

13

.

Test

CIRCUIT DESCRIPTION

The A5347CA is a low-current CMOS circuit providing all of the

required features for an ionization-type smoke detector.

Oscillator. An internal oscillator operates with a period of 1.67

seconds during no-smoke conditions. Every 1.67 seconds, internal

power is applied to the entire circuit and a check is made for smoke.

Every 24 clock cycles (40 seconds), the LED is pulsed and a check

Since very-low currents are used in the device, the oscillator capacitor

at pin 12 should be a low-leakage type (PTFE, polystyrene, or

polypropylene).

Detector Circuitry. When smoke is detected, the resistor divider

network that sets the sensitivity (smoke trip point) is altered to increase

the sensitivity set voltage (pin 13) by typically 130 mV with no external

connections to pins 3 or 13. This provides hysteresis and reduces

false triggering. An active guard is provided on both pins adjacent to

the detector input (pin 15). The voltage at pins 14 and 16 will be within

100 mV of the input. This will keep surface leakage currents to a

minimum and provide a method of measuring the input voltage without

loading the ionization chamber. The active guard amplifier is not

power strobed and thus provides constant protection from surface

leakage currents. The detector input has internal diode protection

against static damage.