A5364 데이터 시트보기 (PDF) - Allegro MicroSystems

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A5364

SMOKE DETECTOR WITH INTERCONNECT

Allegro MicroSystems 

5364

SMOKE DETECTOR

WITH INTERCONNECT

ELECTRICAL CHARACTERISTICS (continued)

Characteristic

I/O Current

I/O Alarm Voltage

I/O Delay

Supply Current

Test

Pin

2

2

2

6

Test Conditions

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

Min.

25

-7.5

3.0

—

—

—

Limits

Typ. Max.

—

60

—

—

—

—

3.0

—

5.0

9.0

—

12

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.

Units

µA

mA

V

s

µA

µA

CIRCUIT DESCRIPTION

The A5364CA 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 VDD to an internal reference.

Because 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 external connec-

tions 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 0.5 s

ON, 0.5 s OFF, 0.5 s ON, 0.5 s OFF, 0.5 s ON, 1.5 s OFF (temporal

horn pattern). During the OFF time, smoke is 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.

Sensitivity Adjust. The detector sensitivity to smoke is set inter-

nally by a voltage divider connected between VDD and VSS. The

sensitivity can be externally adjusted to the individual characteristics of

the ionization chamber by connecting a resistor between pin 13 and

VDD, or between pin 13 and VSS.

Low Battery. The low battery threshold is set internally by a voltage

divider connected between VDD and VSS. The threshold can be in-

creased by connecting a resistor between pin 3 and VDD. The threshold

can be decreased by connecting a resistor between pin 3 and VSS. The

battery voltage level is checked every 40 seconds during the 10 mA,

10 ms LED pulse. If an LED is not used, it should be replaced with an

equivalent resistor (typically 500 Ω to 1000 Ω) such that the battery

loading remains at 10 mA.

115 Northeast Cutoff, Box 15036

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

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