CN-0537

Circuit Note

Rev. A | Page 2 of 8

Figure 1. CN-0537 Block Diagram

CIRCUIT DESCRIPTION

Smoke Detection Using the ADPD188BI

The ADPD188BI optical module is a complete photometric

system specifically designed for smoke detection applications.

Using the ADPD188BI in place of traditional, discrete smoke

detector circuits greatly simplifies the design as the opto-

electronics (consisting of two LEDs and two photodetectors)

and the analog front end (AFE) are already integrated into

the package.

To perform smoke detection, the ADPD188BI utilizes a dual-

wavelength technique: two integrated LEDs emit light at two

different wavelengths and one LED at 470 nm (blue light) and

the other LED at 850 nm (infrared light). These LEDs are

pulsed in two independent time slots, and the transmitted light is

scattered back onto the device by particulate matter in the air.

Figure 2. Backscattering of Light from ADPD188BI LEDs

Two integrated photodetectors then receive the scattered light

and produce proportional levels of output current, which are

converted internally by the AFE into digital code. Assuming the

LED optical power is kept constant, an increase in ADPD188BI

output values over time indicates an increase or buildup in

airborne particles.

UL 217 and UL 268 Smoke and Fire Test Algorithm

The UL 217 and UL 268 standards require detectors to respond

to different types of fire and smoke within a specific window

of time and obscuration. Table 1 lists the obscuration

percentage and response time requirements for each UL 217

and UL 268 test.

Table 1. Fire Conditions and Specifications

Fire Condition

Alarm Time

Specification1

Alarm

Obscuration

Specification1

Wood Fire

<4 minutes

N/A

Paper Fire

<4 minutes

N/A

Polyurethane Fire

<4 minutes

<5 % per foot

Smoldering

Polyurethane Fire

N/A

<12 % per foot

Smoldering Wood

N/A

<10 % per foot

Hamburger Nuisance

Test

N/A

Not before

<1.5% per foot

1

N/A means not applicable.

For the CN-0537 reference design, these specifications are

met by analyzing the blue and infrared (IR) output data of the

ADPD188BI through a smoke detection algorithm.

ADP151-1.8

VDD1

SCATTERED BLUE/IR LIGHT

SMOKE CHAMBER

+5V

+3.3V

+3.3V

+5V TO +6V

+1.8V

LT8410

SPI INTERFACE

TEMPERATURE

AND

HUMIDITY

SENSOR

TEMPERATURE AND

HUMIDITY DATA

I2C INTERFACE

ENABLE VIA GPIO

VDD2

INTEGRATED OPTICAL MODULE

FOR SMOKE DETECTION

VLED3

BLUE/IR

DATA

VLED1

PDET2

PDET1

PDC

ADPD188BI

VLED3

IR

BLUE

VLED1

EMITTED BLUE/IR LIGHT

VDD

+3.3V

MICRO-SD CARD

BLUE/IR DATA

ADICUP3029 WITH

SMOKE AND FIRE

DETECTION ALGORITHM

VDD

HEATER_EN

+5V

HEATING RESISTORS

BUZZER_EN

BUZZER

LED_EN

ALARM LED

TEST BUTTON

+5V

ALARM INDICATORS

+5V

NOT REQUIRED FOR

THE REGULATIONS

OPTIONAL BOOST

REGULATOR

LIGHT SOURCE (L)

RECEIVER INCLUDING

DETECTOR (S)