Sensors

Temperature sensor design challenges

Temperature monitoring and protection e-book

With over 40 years' experience helping customers optimize their temperature monitoring and protection designs, we've developed a comprehensive e-book covering six unique application challenges involving unique sensor placement and routing considerations. In the Temperature Monitoring and Protection e-book you will learn the design fundamentals of temperature sensing in real-world applications. The  application notes and reference designs provide support and deep insights about the sensor selection process and the considerations required for optimal temperature response.

Topics include:

  • Fundamentals of temperature sensing
  • System temperature monitoring
  • Ambient temperature monitoring
  • Temperature threshold detection
  • Temperature compensation and calibration
  • Body temperature monitoring
  • Fluid temperature monitoring

System temperature monitoring

For many system designs, it is necessary to monitor high-power components (processors, FPGAs, FETs, etc.) to ensure system and user safety. Accuracy of the temperature reading is important, as it enables designers to push performance closer to safety limits or reduce system costs by avoiding overdesigning elsewhere. Our broad portfolio of accurate compact temperature sensors allows the closest placement to these critical components for the most accurate measurements.

System temperature monitoring resources

Title
Type
How to monitor board temperature
Some components, such as FETs, on a PCB require temperature monitoring to improve reliability and overall efficiency of systems. This application note provides details on layout and sensor selection for such system monitoring design challenges.
Application note
High-performance processor die temperature monitoring
FPGA and processor performance can be significantly improved through die temperature monitoring. Such system temperature monitoring can be performed by remote BJT monitoring or with local temperature monitoring.
Application note
Temperature sensors: PCB guidelines for surface mount devices
This application note explains methods for improving the accuracy of the temperature point being measured. The report details layout techniques, device orientation, and best practices for mounting temperature sensors to optimize component temperaturemeasurement.
Application note
Optical sense backlight reference design with temperature sensing
LCD displays have sensitive thermal requirements. This reference design demonstrates LCD temperature monitoring using remote temperature sensors. With system temperature monitoring, when a temperature threshold cross over is observed, a thermal shutdown is initiated to protect the system.
Reference design
Automotive multiple channel temperature sensing for LED headlight reference design
This automotive headlight reference design demonstrates temperature monitoring for a string of matrix LEDs. This design demonstrates the use of remote temperature sensors instead of negative temperature coefficient (NTC) thermistors, significantly reducing the number of components, physical wires, and pins used on a microcontroller.
Reference design

Featured temperature sensors for system temperature monitoring

TMP451

Local and remote temperature measurement (±1°C) with the ability to monitor discrete BJTs (bipolar junction transistors) across the system, or substrate thermal transistors/diodes within a processor

TMP1075

High-accuracy (±2°C) upgrade to industry standard LM75 / TMP75 I2C temperature sensor offering up to 4x lower power

TMP103

Cost-efficient digital temperature sensor (±3°C) with I2C or SMBus communication in a small form-factor 0.76mm x 0.76mm package

TMP235

Cost efficient analog temperature sensor offering (±4°C), which can be paired with an existing ADC

Ambient temperature monitoring

Ambient air-temperature monitoring is critical in many applications to control environmental conditions or ensure safe operating conditions. Accurately and quickly measuring ambient temperature can often be a challenge because the sensor may not be completely exposed to the external environment and subject to self-heating effects from other components in the system. Our family of high-accuracy, low-power single and multi-channel temperature sensors in compact packages enables faster thermal response.

Ambient temperature monitoring resources

Title
Type
Layout considerations for accurately measuring ambient temperature
Ambient temperature monitoring requires specific layout and package considerations for temperature sensors. Without careful design considerations, errors can be introduced in the accuracy of the ambient temperature in operating environments.
Application note
Smart thermostat localized heat compensation for ambient temperature sensing
Localized thermostat heat generation is a leading cause for incorrect ambient temperature sensing near the return air plenum. This ultimately leads to overshoot in the HVAC cycle, resulting in costly energy bills. This reference design uses low-cost, high-accuracy analog temperature sensor to addresses this thermostat design challenge  to assess the true ambient temperature value.
Reference design

Featured temperature sensors for ambient temperature monitoring

TMP112

NIST traceable digital temperature sensor pairing high-accuracy (±0.5°C) with low power. I2C, SMBus or two-wire communication can be used

LMT01

High-accuracy (±0.5°C), 2-pin temperature sensor with an easy-to-use pulse count current loop interface. Availability in a TO-92 package offers off-board temperature measurement

TMP103

Cost-efficient digital temperature sensor (±3°C) with I2C or SMBus communication in a small form-factor 0.76mm x 0.76mm package

TMP235

Cost efficient analog temperature sensor offering (±4°C), which can be paired with an existing ADC

Temperature threshold detection

For some applications, continuous temperature collection is unnecessary, but it's critical for the system to stay above or below a temperature threshold. Our family of temperature switches and digital temperature sensors enable simple autonomous temperature monitoring to detect with hysteresis when the temperature crosses its limits. Easily design with a selection of devices that allows threshold trip points to be set via an external resistor, pin-programmable, factory-programed or over I2C.

Temperature threshold detection resources

Title
Type
How to protect control systems from thermal damage
Autonomous temperature protection can enable control systems to improve reliability. By enabling an alert to the control loop, threshold detection can not only improve robustness of the system but also save system size through integration.
Application note
Basic fan controller with over-temperature detection
Temperature threshold detection for over temperature conditions are in personal electronics, industrial PCs and power distribution units to control fans for thermal conditioning. This reference design demonstrates an integrated, small size temperature switch for threshold detection, optimizing the number of components required for basic fan control.
Reference design
60W, 24V high efficiency industrial power supply with precision voltage, current and power limit
60-W, industrial AC-DC power supplies are designed for use in industrial and instrumentation systems such as process controls, factory automation, and machinery control. This reference design is a Quasi-resonant (QR) flyback converter implemented with optocoupled feedback for voltage and primary-side regulation (PSR) for constant current regulation. With a pin selectable temperature switch, the trip point can be selected for threshold detection to protect the power supply.
Reference design
Low-power battery temperature monitoring
Battery charging has a direct dependence on temperature, which is why batteries specify a Temperature-range where charging is most efficient. Charging outside the specified temperature presents safety risks. To prevent charging when the temperature is too hotor too cold, a temperature sensor and corresponding circuitry are required to disable the charging circuit. With use of temperature switch, an over- or under-temperature condition based on factory-programmed trip points is detected. This local temperature threshold signal isused to disable the charging circuit, protecting the battery systems.
Application note

Featured temperature sensors for temperature threshold detction

TMP302

Temperature switch offering pin-selectable threshold trip point for maximum flexibility in systems leveraging an MCU or processor

TMP390

Temperature switch with factory programmed temperature window comparator to minimize external system components

TMP708

Temperature switch offering resistor-configurable threshold trip point for maximum flexibility in systems that do not have an MCU or processor available

Temperature compensation and calibration

Temperature drift must be a factor in correcting temperature shifts in any system. Temperature will affect everything from passive components (resistors and capacitors, etc.) to active components (amplifiers, data converters, references, clocks, etc.). Even optical components are subject to temperature drift, which changes intensity, spectral shifts, or sensitivity and noise. Our highly linear, high-accuracy temperature sensors provide designers the temperature feedback to correct the effects of temperature in precision systems.

Temperature compensation & calibration resources

Title
Type
Methods to calibrate thermal monitoring systems
Temperature sensors are affected by various environmental effects aside from manufacturing process variations. These include thermal stress, mechanical stress, radiation, humidity, and aging during storage, shipment, and/or assembly that may alter the device’s intrinsic characteristics such as accuracy and reliability - after it is implemented on the final system. Both environmental and system electrical factors may require system calibration to achieve a definite system accuracy.
Application note
Replacing RTDs with digital temperature sensors in high accuracy sensing and compensation systems 
Temperature compensation applications require ultra-high accuracy. Resistance temperature detectors (RTDs) offer high linearity across a wide temperature range. 3-wire or 4-wire RTD circuits often involve complex design and calibration. The ±0.1°C accuracy digital temperature sensors offer high accuracy and linearity with no calibration requirements. This application report outlines the design considerations for RTD replacement using a silicon based temperature sensor.
Application note
Automotive high-temperature sensor (HTS) reference design
This reference design demonstrates a thermocouple analog front end. The protection strategies involved in the design protect the analog front end from coupling transients. The digital temperature sensor with high accuracy of < ±1°C is used as a reference to aid in compensation for the cold-junction compensation circuit.
Reference design
Temperature sensor interface module for programmable logic controllers (PLC)
This reference design provides a detailed assessment on sensor signal conditioning, thermocouple cold junction compensation, a ratiometric measurement technique for RTD, recommended software flow, sensor linearization, sensor diagnostics, transient protection, PCB layout and other practical design considerations for achieving high precision robust design for temperature measurement in industrial applications.  The Temperature Sensor Interface Module is a fully isolated design, which is essential for small sensor signal measurement. This design is also compliant with IEC61000-4 which is needed for reliable performance in harsh/noisy industrial environments.
Reference design
RTD replacement for cold junction compensation in a temperature sensor
Temperature sensing applications that use a thermocouples require an accurate local temperature sensor to achieve high accuracy. Solutions for design challenges such as cold-junction compensation (CJC) or including an ultra-low power thermocouple analog front-end are addressed in this reference design. Performance in terms of power consumption and accuracy is optimized for accurate 4 to 20 mA sensors while also demonstrating the performance of different CJC and TC front-end implementations.
Reference design

Featured temperature sensors for temperature compensation and calibration

TMP117

NIST traceable, Single chip digital temperature sensor enabling class AA RTD replacement with high accuracy (±0.1°C) and no calibration

LMT70

Ultra-small 0.88mm x 0.88mm analog temperature sensor offering high accuracy (±0.2°C) in systems with an ADC available

TMP112

NIST traceable digital temperature sensor pairing high-accuracy (±0.5°C) with low power. I2C, SMBus or two-wire communication can be used

TMP235

Cost efficient analog temperature sensor offering (±4°C), which can be paired with an existing ADC

Body temperature monitoring

Understanding a patient's temperature is a critical first step in any clinical diagnosis and an important concern for athletes. Beyond the need for ultra-high accuracy, industry trends are moving toward compact wearable form factors to provide continuous temperature monitoring. Temperature sensors with up to 0.1°C accuracy not only meet ASTM E1112 requirements for medical thermometers but also are optimized to keep battery-powered wearables compact and comfortable.

Body temperature monitoring resources

Title
Type
Enabling research in wireless patient monitoring with the University of California
Texas Instruments & the University of California discuss the value of advancing medical temperature monitoring using ultra-high-accuracy digital temperature sensors.
Video
Layout considerations for wearable temperature sensing
High-accuracy body temperature measurement requires careful design considerations to improve thermal response time without compromising on the accuracy of the system. Sensor placement, flexible PCB and connectivity are a few features that are instrumental in enabling body temperature measurement.
Application note
Bluetooth-enabled high accuracy skin temperature measurement flex PCB patch
The American Society for Testing and Materials (ASTM) require as much as ±0.1°C accuracy from the system for optimal patient’s temperature monitoring. Expansion of the Internet of Things has enabled aggregation of data using wireless technology. Design of temperature patches with such wireless technology requires careful consideration of flexible PCB design, sensor placement and routing. This reference design walks through these aspects of design while enabling long battery life with wireless technology.
Reference design

Featured temperature sensors for body temperature monitoring

TMP117

NIST traceable, ASTM E1112 & ISO 80601 compliant, high accuracy (±0.1°C) digital temperature sensor with transmission over either I2C or SMBus

LMT70

Ultra-small 0.88mm x 0.88mm analog temperature sensor offering high accuracy (±0.2°C) in systems with an ADC available

Fluid temperature monitoring

For many metering and industrial processes, it's necessary to either have a direct measure of a fluid's temperature or use the temperature data for compensation purposes to more accurately calculate the volumetric rate of flow. These applications require the sensors not only be small to reduce resistance in the flow, but also low power in cases where the fluid is flammable. We offer low-power analog and digital solutions with accuracy comparable to Class AA RTDs that draw as little as 6.3µW.

Fluid temperature monitoring resources

Title
Type
RTD replacement in heat meters using digital temperature sensors
Heat meters that measure water temperature require ultra-high accuracy. Resistance temperature detectors (RTDs) offer high linearity across a wide temperature range, however these sensors require calibration and compensation to attain repeatability with accuracy. ±0.1°C accuracy digital temperature sensors offer high accuracy and linearity with no calibration needs. This application report outlines the design considerations for RTD replacement using silicon based temperature sensors.
Application note
Replacing platinum RTD sensors with digital temperature sensors
Heat meter temperature probes require ultra-high accuracy,. This reference design uses a digital temperature sensor with accuracy comparable to a Class-AA resistance temperature detector (RTD). 
Reference design
Reference design

Featured temperature sensors for fluid temperature monitoring

TMP117

NIST traceable, high accuracy (±0.1°C) digital temperature sensor with transmission over either I2C or SMBus.

TMP112

NIST traceable digital temperature sensor pairing high-accuracy (±0.5°C) with low power. I2C, SMBus or two-wire communication can be used

LMT01

High-accuracy (±0.5°C), 2-pin temperature sensor with an easy-to-use pulse count current loop interface. Availability in a TO-92 package offers off-board temperature measurement