RE46C145 查看數據表（PDF） - Microchip Technology

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RE46C145

CMOS Photoelectric Smoke Detector ASIC with Interconnect and Timer Mode

Microchip Technology 

RE46C145

3.6 Low Battery Detection

In standby, an internal reference is compared to the

voltage divided VDD supply. A low battery status is

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

If resistors RADJ1 and RADJ2 are in place and a high-to-

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

internal VDD - 3.5V reference to the voltage that

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.

If VSEN is left unconnected or tied to VSS, the Timer

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

VSS and sourcing ~200 µA out of the pin for 1 clock

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:

Pin Name

IO

VSEN

FEED

COSC

HORNB

LED

DIAGNOSTIC MODE PIN FUNCTION

Pin

Number

7

15

10

12

8

11

Function

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.

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

down device is disabled. .

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.

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

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

condition has been detected.

The LED pin is used as a low battery indicator. For VDD above the low battery thresh-

old, the open drain NMOS is off. If VDD falls below the threshold, the NMOS turns on.

DS22181C-page 10

 2009-2012 Microchip Technology Inc.

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