CS235

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


Pinout




Specifications

Lead Temperature Soldering
Wave Solder (through hole styles only) ............................................................10 sec. max, 260 peak
Reflow (SMD styles only) ..............................................................60 sec. max above 183, 230 peak
Storage Temperature Range ................................................................................................-65 to 150


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.

CS235 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.

CS235 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 ICC current limiter. CS235 current limiter eliminates power-on false alarming.

The oscillator CS235 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 CS235 is capable of sinking  100 milliamps maximum and will clamp the VCC pin 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.