A5354 데이터 시트보기 (PDF) - Allegro MicroSystems

부품명

상세내역

제조사

A5354

SMOKE DETECTOR WITH INTERCONNECT

Allegro MicroSystems 

5354

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

V = 9.0 V, No Alarm, No Loads

DD

V = 12 V, No Alarm, No Loads

DD

Min.

25

-7.5

3.0

—

—

—

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.

Limits

Typ. Max.

—

60

—

—

—

—

3.0

—

5.0

9.0

—

12

Units

µA

mA

V

s

µA

µA

CIRCUIT DESCRIPTION

The A5354CA 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 de-

tected, 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 hyster-

esis 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.

Sensitivity Adjust. The detector sensitivity to smoke is set internally

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 thresh-

old 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

Share Link: