The AD590 is a dual-ended integrated circuit temperature sensor whose output current is proportional to the absolute temperature. For supply voltages of 4v to 30v, the device acts as a high-impedance constant-current regulator through 1μA /K. The laser trimmed chip's film resistance was used to calibrate the device's 298.2μA output at 298.2K (25°C).
Schematic Diagram
The AD590 is intended for use in any temperature sensing application below 150°C, where conventional electrical temperature sensors are currently used. The inherent low cost of monolithic integrated circuits combined with the elimination of support circuits makes the AD590 an attractive alternative for many temperature measurement situations.
The application of the AD590 eliminates the need for linearization circuits, precision voltage amplifiers, resistance measurement circuits, and cold junction compensation. In addition to temperature measurements, applications include temperature compensation or calibration of discrete components, bias proportional to absolute temperature, flow velocity measurements, fluid level detection and wind velocity measurements.
Temperature scale conversion equation 
The AD590 comes in die form and is suitable for rapid temperature measurement in hybrid circuits and protected environments. The AD590 is particularly useful in remote sensing applications. Due to its high impedance current output, the device is not sensitive to voltage drops over long lines. Any well-insulated twisted pair is sufficient to operate hundreds of feet from the receiving circuit. Output features also make the AD590 easy to reuse: The current can be switched by a CMOS multiplexer, or the supply voltage can be switched by a logic gate output.
