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2012-03-28

PHOTOELECTRIC SMOKE DETECTOR

WITH INTERCONNECT

SMOKE DETECTOR

M75310

一華半導體股份有限公司

MOSDESIGN SEMICONDUCTOR CORP.

PIN AND CIRCUIT DESCRIPTION

Pin No

Pin Name

Description

1C1

A capacitor connected to this pin determines the gain of the photo amplifier during the push-to-test mode and

during the chamber monitor test. A typical value for this high-gain mode is 0.047μF but should be selected

based on the photo chamber background reflections reaching the detector and the desired level of sensitivity.

Ae ≒ 1 + ( C1 / 10 ) where C1 is in pF. Ae should not exceed 10,000.

2C2

A capacitor connected to this pin determines the gain of the photo amplifier during standby. A typical value for

this low-gain mode is 4700 pF but should be selected based on a specific photo chamber and the desired level

of sensitivity to smoke. Ae ≒ 1 + ( C2 / 10 ) where C2 is in pF. Ae should not exceed 10,000.

3

DETECT

This is the input to the photo amplifier and is connected to the cathode of the photo diode. The photo diode is

operated at zero bias and should have low dark leakage current and low capacitance.

4STROBE

This output provides a strobed, regulated voltage of VDD-5V. The minus side of all internal and external

photo amplifier circuitry is referenced to this pin.

5

VDD

This pin is connected to the most-positive supply potential.

6IRED

This output provides a pulsed base current for the external NPN transistor, which drives the IR emitter. Its beta

should be greater than 100. The IRED output is not active, to minimize noise impact, when the horn and

visible LED outputs are active.

7I/O

A connection at this pin allows multiple smoke detectors to be interconnected. If a local smoke condition

occurs, this pin is driven high. As an input, this pin is sampled nominally every 1.35 seconds during standby.

Any local-alarm condition causes this pin to be ignored as an input.

An internal NMOS device acts as a charge dump to aid in applications involving a large (distributed)

capacitance. The charge dump is activated at the end of local or test alarm. This pin also has an on-chip pull-

down resistor and must be left unconnected if not used. In application, there is a series current-limiting resistor

to other smoke alarms.

8

HORN1

9

HORN2

10

FEEDBACK

These three pins are used in conjunction with external passive components and a self-resonating piezoelectric

transducer. HORN1 is connected to the piezo metal support electrode; the complementary output, HORN2, is

connected to the ceramic electrode and the FEEDBACK input to the feedback electrode.

A continuous modulated tone indicates either a local or remote alarm condition. A short (10ms) chirp indicates

a low-battery chirp occurs almost simultaneous with the visible LED flash. If the FEEDBACK pin is not used,

it must be connected to VDD or VSS.

11

LED

This open-drain NMOS output is used to directly drive a visible LED. The low-battery test does not occur

coincident 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 seconds.

Remote Alarm ─ No pulses.

Test Mode ─ Pulses every 0.67 seconds.

12

OSCC

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.

13

OSCR

A resistor between this pin and OSCC (pin 12) is part of the two-terminal oscillator and sets the internal clock

high time, which is also the I

RED pulse width. With component values as shown , this nominal time is 105μs .

14

VSS

This pin is connected to the most negative supply potential (usually ground).

15

TRIP

This pin is connected to an external voltage, which determines the low-supply alarm threshold. The trip

voltage is obtained through a resistor divider connected between the VDD and LED pins. The low-supply

alarm threshold voltage ( in volts ) ≒ ( 5R15/R14 ) + 5 where R15 and R14 are in the same units.

16

TEST

This pin has an internal pull-down device and is used to manually invoke a test 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 cycle, I

RED pulse 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 I

RED 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 I

RED pulse

(less than one second), the device exits this mode and returns to standby.