Designing with IC temperature sensors

Previous columns examined thermistors, RTDs (resistance-temperature detectors), and thermocouple temperature sensors. The integrated temperature sensors on the market can also solve temperature woes (Figure 1). These sensors operate over a temperature range of only −55°C to 200°C. However, they are easy to install on PCBs, and they have a user-friendly output format. It is difficult to categorize the various types of IC sensors, but the following paragraphs take a stab at describing the generalities of the inputs, insides, and outputs of these silicon chips.



IC temperature sensors have a variety of input and output options. For instance, an IC temperature sensor that has the actual temperature sensor within the silicon chip can be selected. This sensor reports the temperature at the sensor’s location. In contrast, many IC temperature sensors can be connected to remote diodes and IR sensors. Remote diodes come in handy when choosing an inexpensive way to remotely sense the temperature of electronics or when interfacing with the available microcontroller or processor internal diode.

When temperature information is acquired at the output terminal of these chips, many interfaces, including voltage and current analog output, digital SPI, digital I2C, and PWM are available. The analog voltage- and current-output IC sensors keep signals in the analog domain. For die-hard digital-minded people, however, the temperature information is available in the standard SPI or three-wire formats and in the two-wire I2C and SMBus (system-management-bus) formats. These digital interfaces provide noise immunity with easy PCB-routing alternatives. With these types of digital signals, resolutions as high as 16 bits and temperature accuracies as high as ±0.5°C can be acquired over a limited temperature range, with ±2.5°C, over the full temperature range.

Designers exploit the process technology of these silicon-based ICs to everyone’s advantage. For instance, some of these chips offer overtemperature signal notifications. If the IC sensor can connect to remote diodes, it may also include compensation features for beta, resistance, and eta factor.

These temperature sensors have some limitations. For instance, RTD or thermocouple temperature sensors should be used to sense temperatures lower than −55°C or higher than 200°C. If the design requires high repeatability and accuracy, an RTD is the best option. The IC temperature sensor’s responsiveness to temperature changes depends on the device’s package size; smaller packages respond more quickly. RTDs, thermocouples, and thermistors typically respond in 1sec to 10sec. IC temperature sensors respond in approximately 4sec to 60sec.

IC temperature sensors are attractive because they include on-chip signal-conditioning circuitry. System designers need not worry about linearization, cold-junction compensation, comparators, additional ADCs, or voltage references. This low-cost approach may be exactly what is needed to protect systems in the field.


About the author
Bonnie Baker is a senior applications engineer at Texas Instruments.