A5349 데이터 시트보기 (PDF) - Allegro MicroSystems

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A5349

AC SMOKE DETECTOR WITH INTERCONNECT AND TIMER

Allegro MicroSystems 

5349

AC SMOKE DETECTOR

with INTERCONNECT

and TIMER

ELECTRICAL CHARACTERISTICS continued

Characteristic

LED Output ON Current

LED Output ON Time

LED Output OFF Time

I/O Current

I/O Alarm Voltage

I/O Delay

Supply Current

Test

Pin

5

5

5

2

2

2

6

Test Conditions

VDD = 7.2 V, VOUT = 1.0 V

Local Alarm

Timer Mode, No Alarm

No Alarm, In Standby

No Alarm, Timer Mode After Pin 1

High-to-Low

No Alarm, VI/O = VDD – 2.0 V

Alarm, VI/O = VDD – 2.0 V

External “Alarm” In

“Alarm” Out

VDD = 9.0 V, No Alarm, No Loads

VDD = 12 V, No Alarm, No Loads

Limits

Min.

Typ.

Max.

10

—

—

constant OFF

—

8.35

—

constant ON

—

1.67

—

25

—

60

-7.5

—

—

3.0

—

—

—

3.0

—

—

5.0

9.0

—

—

12

Units

mA

—

s

—

s

µA

mA

V

s

µA

µA

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

NOTE 2: Alarm (Smoke) Condition is defined as V15 < V13; No Alarm (No Smoke) Condition as V15 > V13.

CIRCUIT DESCRIPTION

The A5349CA 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), a check is made for low supply by

comparing VDD to an internal reference. 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 in-

crease 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.

115 Northeast Cutoff, Box 15036

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

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