ELM331

ELM331 Solid State Thermostat Description The ELM331 is a complete temperature measurement and control system in an 8 pin package. This integrated circuit is designed to compare two resistances and drive an output pin depending on the relative value of each. Typically, one of the resistors will be an NTC thermistor, and the other one will be a temperature independent resistor (whether fixed or variable). When the magnitude of the resistance connected to pin 2 exceeds the value of the resistance connected to pin 3, the output pin will be driven to a high state. Hysteresis maintains the output in that state until the relative values differ by approximately 8% (or typically 2°C for a 10KΩ thermistor). To reduce the possibility of sporadic outputs, a condition must exist for three successive cycles, or 6 seconds, before the output pin can change state. Applications Primary thermostat in temperature control systems Staging control for auxiliary heating or cooling installations Under or over temperature alarms Features Low power CMOS design - typically 1mA at 5V Wide supply range - 3.0 to 5.5 volt operation Built-in proportional hysteresis Measurement in progress output Time delay on operate improves noise immunity Internal pullup resistor on the reset input High current drive outputs - up to 25 mA Connection Diagram PDIP and SOIC (top view) VDD 1 R1 2 R2 3 reset 4 8 VSS 7 Out 6 MIP 5 Cap Block Diagram reset 4 2 R1 3 R2 5 VDD Control Watchdog Timer ...