Page 1
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
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
Page 2
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
Page 3
CS235
Electrical Characteristics:
TA= 25¡C
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
3
■ Amplifier A2
DC Output (pin 9) R3 = 6k½, R4 = 510½, C5 = .47µF 2.5 V
Input Bias Current (pin 8) (Externally adjusted gain 250 nA
with R3 and R4. Unity DC gain)
Voltage gain @ 3.5kHz (Externally adjusted gain 21.6 dB
with R3 and R4. Unity DC gain)
■ Detector and Reference Output (C4 = .47µF)
Reference Resistance 13 19 25 k½
Reference Voltage (pin 10) 1.8 3.6 5.5 V
Detector Output Resistance 10 15 20 k½
Detector Output Voltage (pin 11) 1.4 2.8 4.3 V
(No signal, and at 2X time Constant)
■ Main Timer (R1 = 20M½, R2 = 75k½, C1 = .47µF)
Power Up Pulse Period Standby Mode (pin 1) 8 10 12 Sec
Power Up Pulse Period Speed Up Mode (pin 1) 1.5 2 2.5 Sec
Power Up Pulse Width (pin 1) 20 ms
Gate Pulse Width Power up pulse width 12 10 ms
Sink Current (pin 18) V (pin 16) = 16V 415 460 505 nA
Source Current (pin 18) V (pin 16) = 16V -220 -235 -250 µA
■ Output Circuit
Output Latch Voltage (pin 3) I
SUPPLY
= 100mA 4.4 5.2 6.1 V
Leakage Current V (pin 3) = 38V, V (pins 2, 16) = 0V 500 µA
■ Alarm
Alarm Reset Supply interruption 5 Sec
Power up time 30 Sec
System will go into alarm upon detection and transfer of three consecutive alarm level signals into the counter.
Page 4
Power Up
20ms
Gate (Clock)
10ms
3.5KHz
Oscillator/
LED Driver
Comp. Ref.
Comp. Ref.
Level Detector Output
Data Input (low)
Alarm Enable (low)
Preset
10 Sec.
20ms
2 Sec.
Power Up
20ms
Gate (Clock)
10ms
3.5KHz
Oscillator/
LED Driver
Comp. Ref.
Comp. Ref.
Level Detector Output
Data Input
Alarm Enable
Preset
Timing Diagram In AlarmTiming Diagram Out of Alarm
Timing Diagrams
CS235
4
Page 5
CS235
Application Diagram
R4
510W
C5
.47mF
R5
100K
Synchronous
Detector
Output
Latch
Clock
Oscillator
LED
Driver
R8
36W
Status LED
IR LED
Power
UP
Main
Timer
Current
Limit
R6
18k
C3
6.8nF
Gate
C4
.47mF
R9
270k
1nF
C6
R11
150k
A1
Gain =20
A2
+
4
¥
VCC/Output
COMP
CS235
PGnd
-
+
-
1nF
C7
R2
75k
R1
20M
C1
.47mF
C2
150mF
R3
6k
LLGnd
R7
12M
Counter
Ð 3
¥
6
5
15
13
14
1
17
18
16
2
3
9
11
10
8
7
R12
150k
R12
150k
R13
150k
5
Page 6
Thermal Data 18L 18L
SO Wide PDIP
R
QJC
typ 21 29 ûC/W
R
QJA
typ 100 65 ûC/W
6
Rev. 7/6/98
Package Specification
PACKAGE DIMENSIONS IN mm (INCHES)
D
Lead Count Metric English
Max Min Max Min
18L PDIP 23.37 22.35 .920 .880
18L SO Wide 11.75 11.35 .463 .447
PACKAGE THERMAL DATA
CS235
Ordering Information
Part Number Description
CS235GDW18 18L SO
CS235GDWR18 18L SO (tape & reel)
CS235GN18 18L PDIP
© 1999 Cherry Semiconductor Corporation
Cherry Semiconductor Corporation reserves the
right to make changes to the specifications without
notice. Please contact Cherry Semiconductor
Corporation for the latest available information.
Plastic DIP (N); 300 mil wide
0.39 (.015)
MIN.
2.54 (.100) BSC
1.77 (.070)
1.14 (.045)
D
Some 8 and 16 lead
packages may have
1/2 lead at the end
of the package.
All specs are the same.
.203 (.008)
.356 (.014)
REF: JEDEC MS-001
3.68 (.145)
2.92 (.115)
8.26 (.325)
7.62 (.300)
7.11 (.280)
6.10 (.240)
.356 (.014)
.558 (.022)
Surface Mount Wide Body (DW); 300 mil wide
1.27 (.050) BSC
7.60 (.299)
7.40 (.291)
10.65 (.419)
10.00 (.394)
D
0.32 (.013)
0.23 (.009)
1.27 (.050)
0.40 (.016)
REF: JEDEC MS-013
2.49 (.098)
2.24 (.088)
0.51 (.020)
0.33 (.013)
2.65 (.104)
2.35 (.093)
0.30 (.012)
0.10 (.004)
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