Keep Designs Cool with a Tiny, Low-Power Temperature Sensor

November 14, 2017

Ani Fayezi Kerry Lacanette By: Ani Fayezi, and Kerry Lacanette,
Senior Principal Member of Technical Staff, Core Products Group, Maxim Integrated 

What do smartphones, vacuum cleaners, and communications equipment have in common? Each has components that can’t run too hot. Temperature sensors play an important role in making sure that essential circuitry stays cool.

From buildings and homes to appliances, computers, and industrial equipment, each of these things has components that require constant temperature monitoring and control. Temperature sensors are everywhere now, and they come in a variety of types. Some sensors measure ambient air temperature in buildings for climate control. Other sensors can operate in harsh environments, measuring the temperature of liquids like coolants used in automobiles or working their magic inside automated factories. Local temperature sensor ICs use the physical properties of transistors on the die as their sensing element. Level shifters, gain stages, analog-to-digital converters (ADCs), and other circuitry can be used to create a sensor with an analog or digital interface.

For many of today’s designs, the name of the game is all about reducing size and power without detracting from performance or functionality. This challenge is most obvious for any kind of portable, battery-powered equipment. If a processor inside, say, a smartphone or a wearable device overheats, this could cause the design's specifications to change in a detrimental way. So your system needs to be alerted before this becomes problematic. If we’re talking about applications like communications equipment or servers, knowing that a part is running too hot can trigger a corresponding—and necessary—action, such as turning on fans or cutting back on the clock speed of the processor to cool things down.

A Sensor for Nearly Any Space

Maxim has a new local temperature sensor with an average power-supply current under 10µA and available in a 0.84mm x 0.84mm x 0.35mm 4-bump wafer-level package (WLP). Its low-power consumption extends the runtime of coin-cell battery-operated devices, while its tiny footprint fits inside the smallest wearable devices. The IC delivers ±2℃ accuracy over a wide temperature range (-10°C to +105°C). It is also the market’s only temperature sensor with I2C and SMBus 3.0 compatibility, featuring SMBus 3.0 packet error checking (PEC) for reliable data transmission. When used with the right master, PEC helps to avoid communication errors and eliminates the need for the microcontroller to send out commands to assess data integrity, an important consideration for high-reliability systems such as data centers. Its I2C/SMBus-compatible serial interface accepts standard write byte, read byte, send byte, and receive byte commands to read the temperature data and configure the sensor’s behavior. If the clock is low for more than 30ms (nominal), bus timeout resets the interface.

With the MAX31875 temperature sensor, a selectable resolution capability (up to 12 bits) provides the flexibility to trade off between temperature measurement resolution and power, based on design requirements. For example, you can choose to read the temperature more or less frequently and at different resolutions, based on your power budget and temperature precision requirements.

MAX31875 simplified block diagram

MAX31875 diagram

Design Contest: Show Us Your Analog Artistry

So, the next time you're working on a very small, battery-powered design, the MAX31875 provides a good temperature sensing option. For a deeper dive on temperature sensors, check out Maxim’s new Temperature Sensor Tutorial. And, if you’re feeling particularly creative, join the #MakewithMaxim Design Contest featuring the MAX31875. Maxim, All About Circuits, and Mouser are hosting this design contest, presenting you with an opportunity to submit a creative design idea for a chance to win one of your choice from three different development boards: the MikroElektronika Thermo 6 click board featuring MAX31875, the MAX31856EVSYS, or the MAX31865 evaluation kit. You have until November 30 to submit your idea. Judges will choose 125 winners, and these individuals will have until January 5, 2018, to submit a project documenting all aspects of the design using the chosen board. For full contest details and deadlines, visit the All About Circuits #MakewithMaxim Design Contest page.