Sensors

4

Freescale Semiconductor

MC145011

Table 3. AC Electrical Characteristics

C3 = 1500.0 pF, R2 = 10.0 M

Ω)

No.

Characteristic

Symbol

Test Condition

Min

Max

Unit

1

Free-Running Sawtooth

Measured at Pin 12

9.5

11.5

ms

2

LED Status

No Local Smoke, and

No Remote Smoke

Illuminated

3

Remote Smoke, but

No Local Smoke

Illuminated

4

Local Smoke or Push

button Test

Extinguished

5

STROBE Pulse Width

9.5

11.5

ms

6

IRED Pulse Period

Smoke Test

9.67

11.83

s

7

Chamber Sensitivity Test,

without Local Smoke

38.9

47.1

8

Push button Test

0.302

0.370

9

IRED Pulse Width

94

116

µs

10

IRED Rise Time

—

30

µs

IRED Fall Time

—

200

11

SILVER and BRASS Modulation Period

Local or Remote Smoke

297

363

ms

11, 12

SILVER and BRASS Duty Cycle

Local or Remote Smoke

73

77

%

13

SILVER and BRASS Chirp Pulse Period

Low Supply or Degraded

Chamber Sensitivity

38.9

47.1

s

14

SILVER and BRASS Chirp Pulse Width

Low Supply or Degraded

Chamber Sensitivity

9.5

11.5

ms

15

Rising Edge on I/O to Smoke Alarm Response Time

Remote Smoke,

No Local Smoke

—

800

ms

16

Strobe Pulse Period

Smoke Test

9.67

11.83

s

17

Chamber Sensitivity Test,

without Local Smoke

38.9

47.1

18

Low Supply Test,

without Local Smoke

38.9

47.1

19

Push button Test

0.302

0.370

Table 4. Pin Description

Pin No.

Pin Name

Description

1

C1

A capacitor connected to this pin as shown in Figure 8. determines the gain of the on-chip photo amplifier during push

button test and chamber sensitivity test (high gain). The capacitor value is chosen such that the alarm is tripped from

background reflections in the chamber during push button test.

2

C2

A capacitor connected to this pin as shown in Figure 8. determines the gain of the on-chip photo amplifier except during

push button or chamber sensitivity tests.

smoke detections.

Resistor R14 must be installed in series with C2. R14

≈ [1/(12√C2)] - 680 where R14 is in ohms and C2 is in farads.

3

DETECT

This input to the high-gain pulse amplifier is tied to the cathode of an external photodiode. The photodiode should have

low capacitance and low dark leakage current. The diode must be shunted by a load resistor and is operated at zero

bias.

The Detect input must be ac/dc decoupled from all other signals, VDD, and VSS. Lead length and/or foil traces to this

pin must be minimized, also. See Figure 9.