Thank an automotive engineer if you drive a car in a place that juxtaposes multiple major climate zones within a small driving range. Take California, for example, where temperatures in Death Valley reach +55°C and as low as -35°C within a few hours’ drive in Mono County. Just think of all the thermal tolerance that your car and its electronics must have in order to handle these wide temperature ranges – on top of the car’s normal operating extremes seen in body and under-the-hood applications.
No wonder the automotive industry increasingly requires the reliability expected by AEC-Q100 qualified integrated circuit (IC) components. An electronic rearview mirror or tiny, sealed camera module that bakes in the sun all day might requireAEC-Q100 Grade 1components up to 125°C. An engine control unit under the hood increasingly needs Grade 0 components rated for 1,000 hours of operation up to 150°C – and sometimes that’s not even enough. The one component that must be accurate at these extreme temperatures in order to protect the system is no doubt the temperature sensor. Accurate temperature information allows the processor to temperature-compensate the system so that the electronic modules can optimize their performance and maximize their reliability no matter the driving conditions.
IC temperature sensors share a market category with other sensing technologies like thermistors, resistance temperature detectors (RTD) and thermocouples, but ICs have some important benefits when good accuracy is required over wide temperatures like the AEC-Q100 Grade 0 range (-40°C to 150°C). First, the accuracy limits of an IC temperature sensor are given in degrees Celsius in the data sheet across the full operating range; conversely, a typical negative temperature coefficient (NTC) thermistor may only specify the resistance accuracy in percent at a single temperature point. You would then need to carefully calculate the total system accuracy for the full temperature range when using a thermistor. In fact, be careful to check the operating conditions specifying any sensor’s accuracy. For example, generously specified ICs will give the accuracy over the supply-voltage range rather than only at one specific voltage.
Another benefit is that IC temperature sensors are highly linear, which minimizes the need for software compensation. Figure 1 is a linearity comparison of an analog IC temperature sensor and a thermistor.
Figure 1: Linearity comparison of an IC temperature sensor vs. a typical positive temperature coefficient (PTC) thermistor
When selecting an IC, keep in mind that there are several types – with various merits for different automotive applications.
TI’s extensive portfolio of AEC-Q100-qualified temperature sensor products includes devices with extended temperature range offerings. The new LM57-Q1 temperature switch, for example, can sustain operation profiles up to 170°C. This is critical when the system temperature profile requires operating at an extended high temperature.
TI is routinely adding new temperature sensors to our AEC-Q100-qualified device lineup, so watch for new additions.
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