Bench Talk

(Source: Toshiba)

Electronic components are usually designed to function optimally within a given set of parameters, with voltage range, form factor, and board space all representing vital factors developers must consider when creating their designs. One of the biggest design problems to address is operational temperature limits and overheating, especially in applications that include small motors or devices where it would be more cost-effective to replace rather than spend repair time in cases of overheating-related failure. Overheating can also be a design issue in laptop computers and other personal electronic devices that require higher performance in a smaller form factor with each successive generation. Detecting an overheating situation quickly and taking steps to protect the system or device before serious damage can ultimately save users time and money in potential repair and replacement costs and ensure performance reliability.

In this blog, we will examine a simple solution developers can use to detect temperature issues in electronic equipment.

Standard Methods of Temperature Monitoring

Developers often employ thermistors—short for thermal resistors—to detect changes in temperature on a board design. Thermistors don’t operate as well as resistance temperature detectors (RTDs) on the extreme ends of operational temperature ranges. Still, they provide more precision across a narrower temperature range, making them a better option than RTDs for smaller, more intricate mechanisms and devices in which even minute temperature deviations can seriously affect functionality and reliability.

Thermistors fall into one of two categories based on how they react to excessive heat and the materials they’re constructed with: negative temperature coefficient (NTC) and positive temperature coefficient (PTC). NTC thermistors are typically made from powdered iron or nickel oxides and provide less resistance at high temperatures, while PTC thermistors are constructed from alkaline earth metals like barium or strontium and generate more resistance above a specified limit—often at room temperature. PTC thermistors act as a threshold against overheating by only generating resistance above their specified limit, and that resistance becomes an indicator that a specific location within a board or device exceeds the recommended temperature. Systems and motors often have different operating speeds, so preventing overheating damage in these types of applications may be as simple as operating at a lower speed until the internal temperature returns to normal. PTC thermistors used in conjunction with an IC solution can help systems take steps to prevent the harmful effects of overheating and keep components and devices running smoothly.

Toshiba’s Overheating Detection Solution

Toshiba’s Thermoflagger^™ (TCTH0) is an IC designed to be used with PTC thermistors to detect temperature increases and protect components from overheating. Thermoflagger can connect to a PTC thermistor or a series of PTC thermistors by supplying a low-level electric current. Suppose any of the thermistors in the series detects a temperature exceeding its threshold. In that case, the Thermoflagger inverts the FLAG signal from HIGH to LOW until the thermistor no longer reads temperatures exceeding its threshold. Thermoflagger allows developers to incorporate multiple PTC thermistors with different temperature thresholds throughout the board design with very specific operational temperature requirements for each PTC. If the temperature of a single PTC thermistor in the series detects overheating, Thermoflagger will protect the entire board until it's safe to operate again. Thermoflagger provides board designers with greater accuracy and precision and only requires a low current to operate, making it a reliable, low-power IC solution for board designs.

Thermoflagger can be implemented with PTC thermistors in various industrial and electronic applications. By placing PTC thermistors next to MOSFETs or other heat-generating elements on a board, such as inside a PC or laptop, and connecting them to Thermoflagger, the computer can protect itself against system-wide overheating by automatically increasing the fans and throttling individual components down to their recommended operational temperature.

PTCs set for different temperature thresholds can be utilized simultaneously. For example, one MOSFET might have a resistance value of 100°C, while another is set at 60°C. Thermoflagger can simultaneously monitor the temperature at different locations on the board and change the output signal or warn an operator of the overheating event, prompting them to take the necessary steps to ensure device safety and reliability.

Developers can also implement Thermoflagger in small, motorized devices like cordless power drills or handheld vacuum cleaners, for which overheating can often cause irreparable damage. Single or multiple PTC thermistors can be attached to a MOSFET(s) supporting the motor, and Thermoflagger will detect overheating and change output states or alert an external system(s) of the need to take appropriate action until the internal temperature is back within recommended parameters.

Conclusion

The challenge of designing space-efficient, low-cost overheating solutions becomes more significant as devices and form factors become smaller and smaller, and printed circuit board space continues to shrink. PTC thermistors employed on their own can alert developers to overheating issues in their designs, but coupled with an IC solution like Toshiba’s Thermoflagger, can provide more precise, localized, and timely temperature monitoring without the need for other external components.

Thermoflagger, whether used for active temperature monitoring or data analysis to predict heat-related failures, provides developers with a robust, small-footprint, low-cost IC solution to overheating problems in their designs.

Author

Alex Pluemer is a senior technical writer for Wavefront Marketing, specializing in advanced electronics, emerging technologies and responsible technology development.