RE46C180S16TF【PDF 12/58 页】IC ION SMOKE DETECT ASIC 16SOIC

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RE46C180

DS22275A-page 12

?2011 Microchip Technology Inc.

3.4

Push-to-Test (PTT)

PTT is an event when TEST is activated (V

IH3

Release of PTT is an event when TEST is deactivated

IL3

). PTT has different functions for different circum-

stances. In Standby, PTT tests the unit. Upon start of

PTT, the CHAMBER voltage is lowered to a pre-deter-

mined level (user programmable) to emulate a Smoke

condition. The smoke detection rate increases to once

every 250 ms. After three consecutive smoke detec-

tions, the unit will go into a Local Alarm condition. In

alarm, the smoke detection rate decreases to once

every 1s. Upon release of PTT, the unit is immediately

reset out of Local Alarm, and the horn is silenced. The

chamber voltage goes back to the normal standby

level, and the detection rate goes back to once every

10s.

When the unit exits a Local Alarm condition, the alarm

memory latch is set. PTT will activate the alarm mem-

ory indication if the alarm memory latch is set and if the

alarm memory indication function has been enabled. If

the alarm memory indication function has not been

enabled and the alarm memory latch is set, PTT will

test the unit as described above. The release of PTT

will always reset the alarm memory latch.

In Standby and Low Battery conditions, PTT tests the

unit and RLED will be constantly enabled. This allows

the user to easily identify the low battery unit without

waiting for 40s to hear a horn chirp. Upon release of

PTT, RLED goes back to normal standby pulse rate.

The Low Battery HUSH mode is then activated, if this

function is enabled.

3.5

Interconnect Operation

The bidirectional IO pin allows the interconnection of

multiple detectors. In a Local Alarm condition, this pin

is driven high 3.7s after a Local Alarm condition is

sensed through a constant current source. Shorting

this output to ground will not cause excessive current.

The IO is ignored as input during a Local Alarm.

The IO also has an NMOS discharge device that is

active for 0.5s after the conclusion of any type of Local

Alarm. This device helps to quickly discharge any

capacitance associated with the interconnect line.

If a remote active high signal is detected, the device

goes into Remote Alarm and the horn will be active.

RLED will be off, indicating a Remote Alarm condition.

Internal protection circuitry allows the signaling unit to

have higher supply voltage than the signaled unit, with-

out excessive current draw.

The interconnect input has a 291 ms maximum digital

filter. This allows for interconnection to other types of

alarms (CO, for example) that may have a pulsed

interconnect signal.

As a user-programmable option, the smart intercon-

nect (smart IO) function can be selected. If the IO input

is pulsed high twice with a nominal pulse on time

greater than 37 ms and within 5.4s, a CO Alarm condi-

tion is detected, and the CO temporal horn pattern will

sound. The CO temporal pattern will sound at least two

times, if a CO Alarm condition is detected.

3.6

Reduced Sensitivity Mode

(HUSH Mode)

Upon release of PTT, the unit may or may not go into a

HUSH mode, depending on the users selection.

If the hush-in-alarm-only option is selected, then only

the release of PTT in a Local Alarm condition can initi-

ate a HUSH mode. Upon release of PTT, the unit is

immediately reset out of alarm, and the horn is

silenced.

If the hush-in-alarm-only option is not selected, then

anytime a release of PTT occurs, the HUSH mode is

initiated.

In HUSH mode, the smoke sensitivity is lowered to a

pre-determined level, which is user programmable.

RLED is turned on for 10 ms every 10s.

The HUSH mode period is user programmable it can

be either 9 minutes or 80s. After this period times out,

the unit goes back to its standby sensitivity.

If the unit is currently in a HUSH mode, then PTT will

test the unit with the standby sensitivity. Upon release

of PTT, a new HUSH mode will be initiated.

As another user-programmable option, HUSH mode

can be terminated earlier by a smart hush function.

This function allows the HUSH mode to be canceled by

either a high smoke alarm, or a remote smoke alarm.

High smoke alarm is the local smoke alarm caused by

a smoke level that exceeds the reduced sensitivity

level.

3.7

Alarm Memory

Alarm memory is a user-programmable option. If a unit

has entered a Local Alarm, when exiting that Local

Alarm, the alarm memory latch is set. The GLED can

be used to visually identify any unit that had previously

been in a Local Alarm condition. The GLED is pulsed

on three times every 40s. Each GLED pulse is 10 ms

long and 1s spaced from the next pulse. This alarm

memory indication period can be 0, 24, 48 hours or no

limit, depending on the users selection.

The user will be able to identify a unit with an active

alarm memory anytime by PTT. Upon start of PTT, the

alarm memory indication will be activated. Depending

on the users selection, it can be 4 Hz horn chirp, 4 Hz

GLED pulse, or both. Upon release of PTT, the alarm

memory latch will be reset.

Anytime a release of PTT occurs, the alarm memory

latch will be reset. The initial visual GLED indication is

not displayed if a Low Battery condition exists.

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