Thermistors are widely used in temperature detection to avoid equipment overheating which can cause faults. Their applications range from wearable devices and mobile phones to automobiles and industrial equipment. They are important protection devices in electronic products. This article will show you the types and applications of thermistors and the functions and characteristics of NTC thermistors for automobiles introduced by Murata.
Thermistor values vary with temperature
Thermistors are sensor resistors whose values change with temperature, and whose volumes vary significantly with temperature. Thermistors belong to the category of variable resistors and can be used as temperature detectors, circuit switches, inrush suppressors, delays for starting motors, and overheating protection. They are widely used in various electronic devices, such as inrush current limiters, temperature sensors, resettable fuses, and auto-adjustable heaters.
Unlike pure metals used in resistance thermometers, the materials used in thermistors are usually ceramics. Both have different temperature response properties - resistance thermometers are suitable for large temperature ranges and thermistors typically achieve high accuracy within a limited temperature range, typically between -40°C and 150°C.
Thermistors are electronic parts whose resistance varies with temperature. Thermistors are divided into the following two types based on resistance changes, including NTC (negative temperature coefficient) thermistors and PTC (positive temperature coefficient) thermistors. NTC thermistors decrease as the temperature rises and the resistance changes by 3-5%/°C, which can be used for temperature sensing, compensation, and inrush current suppression. PTC thermistor resistance remains constant until a certain temperature, and suddenly increases when it reaches a critical temperature. It can be used for overheating detection, overcurrent protection, inrush current suppression, and heaters. This article focuses on NTC thermistors and their applications in the automotive field.
NTC thermistors are widely used in the automotive industry
NTC thermistors are made of ceramics fired from oxides of manganese (Mn), nickel (Ni), cobalt (Co), etc. The ceramics form electrodes and are usually in the shape of lead and chip. NTC thermistors using ceramic material technology are widely used in automobiles. For example, traditional automotive lighting systems require temperature monitoring. Mass Air Flow or Manifold Absolute Pressure (MAF/MAP) sensors and acceleration sensors also require temperature monitoring, while NEV BMS, inverters, and DC-DC converters require more on-board temperature monitoring.
In addition, NTC thermistors are beginning to be used in autonomously piloted millimeter waves, Lidars, ADAS, and other systems. NTC thermistors are used to detect temperature. When the temperature is too high, active cooling (fan) devices are driven to keep the system with the appropriate temperature conditions to maintain stable operation.
Highly trusted NTC thermistors must be used in the automobile and motorcycle markets
Murata introduced the NCU series NTC thermistor, an SMD temperature sensor, for a highly trustworthy automobile market. The external electrodes of the NCU series are made of copper, improving reliability and preventing electronic migration in high humidity environments. The NCU series is mainly used for high-reliability temperature detection. It enables temperature detection and temperature compensation over a wide range of temperatures, protects devices with poor thermal resistance from thermal damage, and enables devices to operate well with precise accuracy when the temperature rises.
SMD NTC thermistors are the best partners for high-precision semiconductor devices (e.g., image sensors, laser diodes) whose sensitivity and accuracy vary with ambient temperature, so NTC thermistors are used to detect the ambient temperature and compensate. In addition, as the operating time increases and the measured temperature rises, the loss of devices will also increase. NTC thermistors can effectively detect the true temperature of devices to prevent overheating and protect their service life to improve system reliability.
NTC thermistors, on the other hand, can also be used in DC-DC/inverters, OBC systems of electric vehicle (EV) to detect power device temperature, prevent overheating, and protect device service life. The temperature of each (12V/48V) protection unit can be detected to adjust the DCDC converter operation speed and improve safety. NTC thermistors, if used in BMS (Battery Management Systems), can be used to detect cell and BMS substrate temperatures, prevent overheating, and protect devices from shortening their service life.
In lower power electric motorcycle applications, a large number of thermistors are also required on BMS, OBC and converters, such as in digital cluster, LED lighting, AD/DC, DC/DC converter, battery pack, BMS, motor controller, etc., all need to use SMD NTC thermistor for protection to prevent the devices from overheating and improve the operational stability of the systems.
Different specifications of NTC thermistors can meet on-board application requirements
Murata's NTC thermistor specifications are quite diverse and customers can learn about specification characteristics from the product name, which includes product ID, series, size (L x W), temperature characteristics, resistance, resistance tolerance, individual specifications and packaging, including NCU15 series (automotive use) 1.0×0.5mm/0.4×0.2inch (automotive use) and NCU18 series (automotive use) 1.6×0.8mm/0.6×0.3inch (automotive use). You can consult Murata's website for more detailed product specifications and characteristics.
For the automotive application market, Murata also has some recommended combinations of IC and thermistor lists to assist customers in designing using thermistors. Take ADAS applications as an example. If Renesas R-CarH3 chips are used, NCU18XH103F6SRB or NCU15XH103F6SRC thermistors can be used. For IVI/TCU applications, NCU18XH103F6SRB or NCU15XH103F6SRC can be used if Samsung Exynos8890 V3, Renesas R-Car-M3, R-Car-M2, or Qualcomm Snapdragon SA8155. If Mediatek MT2712 is used, NCU18WF104F6SRB or NCU15WF104F6SRC can be used. If you have any other application needs, please contact Murata or Arrow Electronics for more information.
Conclusion
As automobiles become more electronic, both fuel vehicles and hybrid/pure electric vehicles use more and more electronic devices and use more and more electronic parts, which, in the harsh application environment of automobiles, require NTC thermistors to detect temperatures and provide better system safety protection. Murata provides a complete, high-quality NTC thermistor product line that will meet the application needs of the automotive market for high stability.