A5358(1996) 查看數據表（PDF） - Allegro MicroSystems

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A5358
(Rev.:1996)

PHOTOELECTRIC SMOKE DETECTOR WITH INTERCONNECT AND TIMER

Allegro MicroSystems 

5358

PHOTOELECTRIC SMOKE DETECTOR

with INTERCONNECT and TIMER

PIN AND CIRCUIT DESCRIPTION, continued

PIN 11 (LED)

This open-drain NMOS output is used to directly drive

a visible LED. The load for the low-battery test is applied

to this output. The low-battery test does not occur coinci-

dent with any other test or alarm signal. The LED also

indicates detector status as follows (with component

values as in the typical application, all times nominal):

Standby

- Pulses every 43 seconds.

Local Smoke - Pulses every 0.67 second.

Remote Alarm - No pulses.

Test Mode - Pulses every 0.67 second.

Timer Mode - Pulses every 10 seconds.

cycle, IRED pulses every 336 ms (nominal) and amplifier

gain is increased by internal selection of C1. Background

reflections in the smoke chamber can be used to simulate

a smoke condition. After the third IRED pulse, a successful

test (three consecutive simulated smoke conditions)

activates the horn drivers and the I/O pin. When the

push-button is released, the input returns to VSS due to

the internal pull down. After one oscillator cycle, the

amplifier gain returns to normal and after three additional

IRED pulses (less than one second), the device exits this

mode and returns to standby. This high-to-low transition

on pin 16 also resets and starts the 10 minute hush timer

(timer mode).

PIN 12 (OSC. CAP.)

A capacitor between this pin and VDD, along with a

parallel resistor, forms part of a two-terminal oscillator and

sets the internal clock low time. With component values

as shown, this nominal time is 11 ms and essentially the

oscillator period.

PIN 13 (TIMING RES.)

A resistor between this pin and OSC. CAP. (pin 12) is

part of the two-terminal oscillator and sets the internal

clock high time, which is also the IRED pulse width. With

component values as shown, this nominal time is 105 µs.

Pin Name Pin No. Configuration

I/O

7

Disabled as an output. A logic

high on this pin places the photo

amplifier output on pin 1 or pin 2

as determined by pin 15. The

amplifier output appears as

pulses.

PIN 14 (VSS)

This pin is connected to the most negative supply

potential (usually ground).

PIN 15 (HUSH)

This input pin serves two purposes in normal opera-

tion. It serves as an enable for the internal 10-minute

(nominal) timer and also as the reference for the smoke

comparator during the timer mode. This reference is

established by a resistive divider between VDD and

STROBE (RX1 and RX2). This allows the detector to have

a different sensitivity set point during the timer mode. If

the timer mode is not used, this pin can be left open or

connected to VSS, which disables this mode.

PIN 16 (TEST)

This pin has an internal pull-down device and is used

to manually invoke two test modes and a Timer Mode.

The Push-to-Test Mode is initiated by a high logic

level on this pin (usually the depression of a normally

open push-button switch to VDD). After one oscillator

HUSH

15

FEEDBACK 10

OSC. CAP. 12

If the I/O pin is high, this pin

controls the amplifier gain capaci

tor. If pin 15 is low, normal gain is

selected and the amplifier output

is on pin 1. If pin 15 is high,

supervisory gain is selected and

the amplifier output is on pin 2.

If pin 7 is high and pin 15 is low

(normal gain), taking this pin to a

high logic level increases the

amplifier gain by ~10% (hyster-

esis).

This pin may be driven by an

external clock source. Driving

this pin low and high drives the

internal clock low and high. The

external RC network may remain

intact.

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