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: (401)885-3600 Fax: (401)885-5786
Email: info@cherry-semi.com
Web Site: www.cherry-semi.com
A1 IN
(-)
A1 IN
(+)
A1
GATE
GATE BIAS
L.L.
GND
INT
OSC PGM
SYNC
CAP
POWER UP BIAS
NC
BIAS
POWER
UP
OSCILLATOR
A2
OUT
DETECTOR
A2
A2
IN
MAIN
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
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