5348

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

Test

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

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

CIRCUIT DESCRIPTION

The A5348CA 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 is made for low battery by

comparing V

Since very-low currents are used in the

device, the oscillator capacitor at pin 12

should be a low-leakage type (PTFE, polysty-

rene, 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 exter-

nal 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.

Alarm Circuitry. If smoke is detected, the oscillator period changes

to 40 ms and the horn is enabled. The horn output is typically 160 ms

ON, 80 ms OFF. During the OFF time, smoke is again checked and

will inhibit further alarm output if smoke is not sensed. During smoke

conditions the low battery alarm is inhibited and the LED is driven at a

1 Hz rate.