NTC & PTC Thermistor (FSC Series)

FSC Series NTC and PTC Thermistors Overview

Thermistors are temperature-sensitive resistors whose resistance changes significantly as their temperature changes. They are commonly used for temperature sensing, temperature compensation, temperature-threshold detection, and overtemperature protection. Based on their temperature coefficient, thermistors are classified as negative temperature coefficient (NTC) thermistors or positive temperature coefficient (PTC) thermistors. NTC and PTC thermistors have different resistance–temperature characteristics and intended applications and are therefore generally not directly interchangeable.

The resistance of an NTC thermistor typically decreases as temperature increases, making it suitable for continuous temperature sensing, temperature compensation, and thermal monitoring. FSC Series NTC thermistors are available in 0201, 0402, 0603, and 0805 surface-mount packages, with a range of nominal zero-power resistance values at 25°C (R25), B-values, and resistance tolerances. They can be used in consumer electronics, communications equipment, power-management systems, battery systems, industrial control, environmental monitoring, and other applications.

R25 represents the nominal resistance of the device at 25°C under specified zero-power conditions. The B-value describes the resistance–temperature characteristics of the device over a specified temperature interval, but it does not by itself represent measurement accuracy across the entire operating temperature range. Because the resistance–temperature relationship of an NTC thermistor is nonlinear, actual measurement error is also affected by R25 tolerance, B-value tolerance, measurement current, self-heating, mounting location, thermal coupling, and the temperature-conversion method.

The resistance of a PTC thermistor typically increases significantly within a specific temperature range, making it suitable for temperature-threshold detection, overtemperature monitoring, and protection control. FSC Series PTC thermistors are available in 0603 and 0805 surface-mount packages, with a selection of Curie temperatures or characteristic temperature ranges. A PTC thermistor’s Curie temperature, sharp resistance-transition range, and actual system trip temperature are not necessarily the same. The protection threshold should therefore be determined based on the device’s resistance–temperature characteristic curve, detection-circuit parameters, and system thermal conditions.

Selection of an NTC or PTC thermistor should take into account R25, the B-value and its corresponding temperature interval, resistance tolerance, operating temperature, maximum permissible operating voltage, rated power, dissipation factor, thermal time constant, measurement current, and package dimensions. A thermistor directly senses its own temperature, which may differ from the temperature of the object or environment being measured. A response delay may also occur.

System design should therefore account for mounting location, thermal conduction paths, airflow, electrical isolation, and other relevant factors. Final device selection and circuit design should be based on the official datasheet for the applicable model.