SENSORS & SENSING SYSTEMS


FEATURE


G THE RIGHT TEMPERATURE UR APPLICATION


Figure 2. Low power temperature sensors vs. accuracy


behaviour of the sensor. The MAX31875 is available in a 4-ball, wafer-level package (WLP) and operates over the -50˚C to +150˚C temperature range.


CPU, FPGA, ASIC, ETC. (WITH ON-BOARD THERMAL DIODE) In order to safeguard high performance ICs like CPUs, FPGAs, and ASICs, semiconductor manufacturers incorporate a temperature-sensing diode-connected bipolar transistor. Since the thermal sensing transistor


sensors can reduce the amount of time needed for charging and extending battery life, yet they maintain their accuracy. Figure 2 (above) exhibits the latest low power temperature sensors vs. their accuracy. The MAX31875 is a ±1˚C accurate local temperature sensor with an I2


C/SMBus interface.


It uses <10µA average power supply current. A typical application circuit is shown in Figure 3.


The combination of extra small package size, excellent temperature measurement accuracy, and very low supply current consumption makes this product ideal for a variety of equipment, especially for battery-operated and wearable devices. The I2


C/SMBus-compatible serial


interface accepts standard write byte, read byte, send byte, and receive byte commands to read the temperature data and configure the


is placed on the IC die, the measurement accuracy is significantly higher than with other sensing techniques. ADI offers several ICs made expressly to detect a thermal diode’s temperature precisely and convert it to digital form. While some of these devices measure just one thermal diode, others can measure up to four or even eight. Figure 4 shows a few of these types of ICs, including the MAX6654, MAX6655/MAX6656, MAX31730, MAX31732, and MAX6581. Remote diode sensors can be widely


employed in electrically noisy environments such as displays, clock generators, memory buses, and PCI buses. An example of a remote diode sensor is


shown in Figure 5. The MAX31732 is the latest multichannel temperature sensor that monitors


its own temperature and the temperatures of up to four external diode-connected transistors. A resistance cancellation feature compensates for high series resistance between circuit-board traces and the external thermal diode, while beta compensation corrects for temperature-measurement errors due to low beta sensing transistors. This device offers two open-drain, active-low alarm outputs that monitor the primary over/under temperature threshold levels, respectively. A non-volatile memory (NVM) allows the sensor to programme the configuration registers during power up without software/firmware intervention. The 2-wire serial interface accepts SMBus protocols (write byte, read byte, send byte, and receive byte) for reading the temperature data and programming the temperature thresholds.


Figure 5. MAX31732 typical application circuit


(Above) Figure 3. The MAX31875 typical application circuit.


CAREFUL CONSIDERATION Choosing the right temperature sensor requires careful consideration of various factors, including application requirements, accuracy, surrounding conditions, output interface, power consumption, and cost. By understanding these factors and evaluating the available options, you can select a sensor that meets your specific needs and ensures accurate and reliable temperature measurements in your application. In fact investing time and effort when specifying the right temperature sensor upfront can lead to improved performance, efficiency, and cost-effectiveness in the long run. Silicon temperature sensors have advanced


significantly, becoming incredibly accurate to allow for a high degree of precision. In order to get exceptional accuracy, IC designers have put a great deal of work into calibrated trimming.


Figure 4. Remote/local multichannel temperature sensors.


Analog Devices www.analog.com


MAY 2025 DESIGN SOLUTIONS 45


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