Toshiba Debuts “Thermoflagger” as Temperature Sensor IC Alternative

Sep 01, 2023

Among the most important considerations in electronic design is thermal management. The goal here is primarily to keep electronics from getting too hot, and a large part of this is actively monitoring temperatures and throttling the system accordingly. Thermal management is particularly important in applications like industrial, where high-power and high temperatures are the norm.

With all that in mind, this week, Toshbia released a new integrated circuit solution dubbed “Thermoflagger” that aims to allow designers to detect overtemperature in their systems and respond accordingly. In this article, we’ll talk about the working principles of thermistors and the details of Toshiba’s new solution.

When it comes to temperature sensing in electronic systems, one of the most standard and popular components is a thermistor.

A thermistor is a temperature sensing device that is made from semiconducting materials. These devices measure temperature by exploiting the principle that a semiconductor material’s resistance will change with temperature. Hence, a thermistor is essentially a temperature-sensitive resistor, which changes in value depending on the temperature to which they’re exposed.

There are two types of thermistors: a negative temperature coefficient (NTC) thermistor and a positive temperature coefficient (PTC) thermistor. NTC thermistors decrease their resistance as temperature increases, while PTC thermistors do the opposite.

Importantly, a thermistor is a non-linear device—meaning that the plot of resistance vs temperature comes out as a curve instead of a straight line. For this reason, in practice thermistor datasheets often provide a table which provides empirically determined temperature-resistance relationships.

Toshiba’s new family of products are designed for making temperature sensing in electronic systems easier for designers.

The new family is called the Thermoflagger family which are over temperature sensing ICs that work in conjunction with PTC thermistors in order to track system temperatures. Within this family, the first two products are the TCTH021BE and the TCTH022BE.

The products work by providing a constant current source output at the PTCO pin, which is then fed to a chain of one or more external PTC thermistors. As the temperature of these thermistors increase, the voltage at the PTCO pin will increase, and that change in voltage is fed to an internal comparator in the IC. In this way, the Thermoflagger IC can detect when a temperature limit is exceeded, and react accordingly.

Should a temperature limit be exceeded, the Thermoflagger ICs will produce a FLAG signal that indicates the overtemperature to a downstream MCU. In the TCTH021BE, the FLAG is not latched, but in the TCTH022BE, the FLAG is latched. More information can be found in the datasheet for the TCTH0xxxE series.

In some thermistor-based temperature sensing setups, each individual thermistor requires its own dedicated IC to read temperature. With the Thermoflagger family, Toshiba is allowing designers to connect multiple PTC thermocouples in series with one Thermoflagger device.

According to the part datasheet, the Thermoflagger family can support up to 30 thermistors connected to one device. Since these parts are in series, if the temperature of any of the thermistors exceeds a given threshold, the device will be able to report to the MCU that an overtemperature has occurred.

A benefit of this approach is that it significantly reduces the amount of discrete ICs required for a robust temperature sensing solution. Additionally, having a single temperature-sensing IC also minimizes the number of connections that are required to an MCU, which in turn reduces system complexity.