RE46C145

DS22181C-page 10

 2009-2012 Microchip Technology Inc.

3.6

Low Battery Detection

In standby, an internal reference is compared to the

latched at the conclusion of the LED pulse. The horn

will chirp for 10 ms every 43 seconds, until the low

battery condition no longer exists. The low battery test

is not performed in a local or remote alarm condition.

The low battery notification does not sound in a local or

remote alarm condition.

3.7

Chamber Fail Detection

In standby, a chamber test is also performed every

43 seconds, by switching to the high gain capacitor C1

and

sensing

the

photo

chamber

background

reflections. Two consecutive chamber test failures will

also cause the horn to chirp for 10 ms every

43 seconds. The low battery chirp occurs just before

the LED pulse (see Figure 3-1). The chamber test and

chamber test failure chirp occurs approximately

21 seconds after the LED pulse. The chamber tests are

not performed in a local or remote alarm condition.

The chamber fail notification does not sound in a local

or remote alarm condition.

3.8

Timer Mode

low transition occurs on the TEST input, the device

enters a 10 minute timer mode. In this mode, the

smoke comparator reference is switched from the

appears on VSEN (pin 15). This allows the sensitivity to

be modified for the duration of the 9 minute timer

period. The chamber test is performed in Timer mode.

mode of operation is inhibited.

3.9

Diagnostic Mode

In addition to the normal function of the TEST input, a

special diagnostic mode is available to calibrate and

test of the smoke detector. Taking the TEST pin below

cycle will enable the diagnostic mode. In the diagnostic

mode, some of the pin functions are redefined. Refer to

Table 3-1 for redefined pin functions in the diagnostic

mode. In addition, in this mode STROBE is always

enabled, and the IRED is pulsed at the clock rate of

10 ms nominal.

TABLE 3-1:

DIAGNOSTIC MODE PIN FUNCTION

Pin Name

Pin

Number

Function

IO

7

The IO pin (7) controls the gain capacitor used for the photo amplifier. If IO is low, then

normal gain is selected. If IO is high, then high gain is selected.

VSEN

15

In Diagnostic mode, the output of the photo amplifier is gated to this pin and the pull-

down device is disabled. .

FEED

10

If the IO pin (7) is low, then taking this input high will enable hysteresis, which is a

nominal 10% gain increase in Normal Gain mode.

COSC

12

If desired, this pin can be driven by an external clock.

HORNB

8

This pin becomes the smoke integrator output. A high level indicates that an alarm

condition has been detected.

LED

11