Cherry Semiconductor CS235GN18, CS235GDWR18, CS235GDW18 Datasheet

Features

■ Synchronous Detection

for High Noise Immunity

■ Pulsed Operation for Low

Average Current Drain

■ System Gain Externally

Set

■ System Sensitivity

Externally Adjustable

■ System Operation

Monitored by Means of
External Red LED

Package Options

CS235

System Photoelectric Smoke Detector

CS235

Description

The CS235 System Smoke Detector
is a photo electric type with a
pulsed infrared LED as the light
source and a silicon photodiode as
the light detector. The CS235 IC,
along with passive external compo­nents, controls the system timing
and signal processing.

Low average current is attained by
pulsing the system once every 10
seconds for 20 milliseconds. Bias is
applied to the signal processing cir­cuitry for this time interval. During
the second half of the pulse, the last
10 milliseconds, the IR LED is
pulsed and the unit samples for an
alarm level smoke condition. After
the first alarm level signal the sam­ple rate increases to a two second
interval. After three consecutive
alarm level samples the logic drives
the output latch signalling the sys­tem panel.

The signal processing circuit blocks

are amplifiers A1 and A2, syn­chronous detector, voltage com­parator and the decode counter.
The voltage gain of A2 and the
comparator reference voltage are
set by external resistors.

Additional on-chip features include
an I

CC

current limiter. The current
limiter eliminates power-on false
alarming.

The oscillator controls the IR LED
excitation frequency and provides
drive to the synchronous detector.
The synchronous detection method
has very high noise rejection perfor­mance.

The internal latch is capable of sink­ing 100 milliamps maximum and
will clamp the VCCpin to 5 volts
when tripped. The latch current is
determined by an external resistor
typically located in the master
panel and is reset by temporary
removal of detector power.

Block Diagram

1

Timer

Pulse Width

2

3

4

5

6

7

8

ICC Program

V

CC

/Output

Hi Level GND

A1 Input (-)

A1 Input (+)

LO Level GND

A2 Input

16

15

14

13

12

11

10

Timer Cap

Timer Period
Program
V REG

LED Output

Oscillator
Program

Internal Bias

NC

Detector Output

9

A2 Output Detector

Reference

17

18

18 Lead PDIP & SOIC Wide

1

A Company

¨

Rev. 7/6/98

Cherry Semiconductor Corporation

2000 South County Trail, East Greenwich, RI 02818

Tel: [phone] Fax: [phone]

Email: [e-mail]

Web Site: www.cherry-semi.com

A1 IN

(-)

A1 IN

(+)

A1

GATE

GATE BIAS

L.L.

GND

INT

OSC
PGM

SYNC

TIMER

CAP

POWER UP BIAS

NC

BIAS

POWER

UP

OSCILLATOR

A2

OUT

DETECTOR

A2

A2

IN

MAIN

TIMER

DET

OUT

PGM

RES

LED

DRIVER

DET
REF

PULSE
WIDTH

COMP

LED H.L.

Gnd

CLOCK

SET

VRI

CURRENT

LIMITER

COUNTER

¥

Ð3

¥

CC

PGM

/

V

CC

OUT

OUTPUT

LATCH

Electrical Characteristics: TA= 25¡C, unless otherwise stated.

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

CS235

2

Absolute Maximum Ratings

Lead Temperature Soldering

Wave Solder (through hole styles only) .....................................................................................10 sec. max, 260¡C peak

Reflow (SMD styles only) ......................................................................................60 sec. max above 183¡C, 230¡C peak

Storage Temperature Range ..................................................................................................................................-65¡C to 150¡C

Absolute Maximum Voltage (pin 3) 38 V
Output Latch Current 100 mA
Operation Temperature 0 70 ¡C

Range, T

A

■ 24V System (C2 = 100 µF, R7 = 12 M½)

Operating Voltage (pin 3) 13.8 22.5 35 V
Average Supply Current V (pin 3) = 22.5V 35 60 µA
Peak Supply Current V (pin 3) = 22.5V )(non Òspeed upÓ) 100 µA
Peak Supply Current V (pin 16) = 12V )(Òspeed upÓ) 150 350 µA
Regulator Voltage (pin 16) 12.8 15.7 V

■ 12V System (C2 = 150µF, R7 = 12M½)

Operating Voltage (pin 3) 8.7 12 V
Average Supply Current V (pin 3) = 12V 60 µA
Peak Supply Current V (pin 3) = 12V (non Òspeed upÓ) 100 µA
Peak Supply Current V (pin 16) = 8V (Òspeed upÓ mode) 350 µA
Regulator Voltage (pin 16) (V pin 3 = 12V) 11.85 V

■ Oscillator

Output Frequency R6 = 18k½, C3 = .0068µF 2.1 3.3 4.4 kHz
Sink Current (pin 14) 16 26 35 µA
Source Current (pin 14) 19 26 32 µA
High Trip Point Voltage (pin 14) 1.8 1.9 2.2 V
Low Trip Point Voltage (pin 14) 1.2 1.4 1.5 V

■ LED Drive (Detector LED and Status LED)

Source Current (pin 15) R8=36½

Detector LED V IR LED = 1.156V 20 30 40 mA
Status LED (alarm) V Status LED = 1.99V 10 mA

Regulator Voltage (pin 15) I

SOURCE

= 30mA 3.7 4.4 5.2 V

■ Amplifier A1

Fixed Gain 26 dB
Input Current B

1

(pin 5) 500 1000 nA

Input Current B

2

(pin 6) 500 1000 nA

Input current (B1-B2) 250 nA