CS235 Datasheet | Cherry Semiconductor Corporation

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 ponents, 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 parator and the decode counter. The voltage gain of A2 and the parator reference voltage are set by external resistors. Additional on-chip features include an ICC 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 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. Features s Synchronous Detection for High Noise Immunity s Pulsed Operation for Low Average Current Drain s System Gain Externally Set s System Sensitivity Externally Adjustable s System Operation Monitored by Means of External Red LED Package Options 18 Lead PDIP & SOIC Wide Timer Pulse Width 1 ICC Program 2 18 17 16 15 14 Timer Cap Timer Period Program V REG Block Diagram INT OSC TIMER PGM PULSE LED H.L. VR ICC VCC/ Gnd BIAS PGM CAP RES WIDTH PGM...