RoadTest: Enroll to Review the Toshiba Thermoflagger™ Over-temperature Detection IC Ref. Board
Author: ZGoode
Creation date:
Evaluation Type: Evaluation Boards
Did you receive all parts the manufacturer stated would be included in the package?: True
What other parts do you consider comparable to this product?: The only components that I can personally think would be directly comparable to the function of this IC would be some of the smaller cheaper microcontrollers acting as an overtemperature monitor. Another alternative could be some kind of comparator circuit, but that would not have the same simplicity to setup as does this solution from Toshiba.
What were the biggest problems encountered?: There were no problems encountered which are worth mentioning. The only complaint I have with the board is the lack of probe points. There was plenty of space on the board and they could have added points to their demo circuit to make easier probing.
Detailed Review:
INTRO (WHAT IS IT?)
The Toshiba Thermoflagger IC is an interesting little chip that can be used for simplifying that use of various PTC sensors. While it is primarily intended for use with PTC thermistors (given the name “Thermo”flagger) it can be used with any PTC; for example force sensors or light sensors. It is a one chip solution that also does not require the use of any analog peripherals meaning it is compatible with pretty much every digital circuit or microcontroller out there. It even allows for monitoring of multiple different locations via one chain of PTC elements and one digital data line based on how it works.
HOW IT WORKS
The TCTH022BE operates by integrating several functions into a single chip, making thermal management both straightforward and easy. Internally, the chip begins its operation by taking the resistance from the connected PTC thermistor and measuring the voltage at which the specified current passes. The Thermoflagger comes in both 1uA and 10uA variants. This voltage is then fed into an internal amplifier that boosts the signal to a level suitable for the chip's processing needs.
The comparator is constantly comparing the incoming voltage signal against a stable reference voltage generated within the chip. This reference voltage is carefully calibrated to correspond to a specific voltage threshold. With the temperature it triggers, set by the selected PTC. Depending on the PTC selected the comparator might trigger at different temperatures.
When the voltage from the PTC thermistor exceeds this reference (indicating that the temperature has crossed the threshold), the comparator trips, changing its output state. This triggers the digital control logic inside the IC, which then drives the output pin either high or low, depending on the design. This output can be connected directly to other digital systems, such as microcontrollers, or used to activate cooling systems or alarms, offering a simple yet effective way to manage over-temperature conditions.
The chip is designed with built-in hysteresis, which is a small temperature buffer that prevents the output from rapidly toggling if the temperature is hovering right around the threshold. This ensures stability and avoids false alarms, which can be a real headache in thermal management systems.
In addition, the TCTH022BE is built to handle a wide range of supply voltages, from 2.7V to 5.5V, without needing any external adjustments. This is thanks to the internal voltage regulation and biasing circuitry that keeps everything running smoothly, even if your power supply isn't perfectly stable. The chip also features a noise filter to clean up any electrical noise that could mess with the temperature readings, which is especially useful in noisy environments.
ALTERNATIVE SOLUTIONS
Discrete Operational Amplifier/Comparator: requires a minimum of three additional components (not including the PTC elements). In addition, due to how this circuit works it will need to be adjusted if there is intention to use it with varying voltage supply levels.
Discrete Biased Transistors: requires a minimum of five additional components (not including the PTC elements). In addition, just like the previously proposed solution it will require adjustment if there is intention to use it with different voltage levels.
Looking at the four different application schematics shown in the datasheet the Thermoflagger requires one or two additional components in addition to the main chip and PTC elements. But where it differs from the previous two discrete solutions is that it can work across the wide voltage range of 1V7 to 5V5 without needing adjustment, allowing the same schematic to be dropped into a variety of designs as a without needing to be redesigned for each application or voltage (other than selecting the correct PTC values based on temperate requirements).
TESTING
I tested the board provided through the roadtest program with the supplied PTC thermistor. I had intended to test it with a photoresistor that I had on hand, but that actually ended up being a phototransistor so it wouldn’t work here. Unfortunately, I did not have a force sensor, but for my potential use cases for an IC like temperature sensing the is most useful application anyways. In future testing I plan on trying to use NTC elements with the Thermoflagger to see if they work in reverse to the intended use as I hypothesize. When I do that testing I plan on updating my roadtest review with that data.
While it was nice of Toshiba to include a totally separate unconnected chip for designing into our own applications, it would be have been nice of them to put in probe points for their demo circuit. I had to solder some wires to the ground leads and PTCGOOD line. By connecting a probe here I was able to look at the stability and rise/fall time.
During my testing the digital output from the Thermoflagger IC appeared to be very stable, which is good since it would prevent any false positives from occurring and causing problems or resetting any circuits. As can be seen in the screengrab from my scope, there is not much if any noise at the highs, lows, and transition points. All around a very smooth signal that does not require any additional filtering. The reaction time of the chip also appeared to be very quick, with the fall time and rise time appearing to be about 2uS.
USE CASES
Toshiba advertises this primarily for use in portable devices and power supplies for easy monitoring of multiple components at once. When at least one device in the chain is triggered as failed, this method assumes all failed or is overtemperature as a failsafe. While this makes the circuit and applications simple, this is unfortunately also the drawback of this particular component.
In this image provided by Toshiba, they also show the Thermoflagger not being used as the primary temperature monitoring, but more as a check to ensure that various temperature monitoring solutions have not failed. So more as a backup than a primary solution here.
While Toshiba advertises this for use in monitoring for overtemperature faults, I can see myself most using a chip like this for monitoring when a temperature hits the acceptable temperature. Using two Thermoflaggers in parallel it can be an accurate and easy way to monitor a temperature window without having to deal with calibrating a voltage reference and/or utilizing a microcontroller with an ADC.
Another application that might be interesting to pursue is to instead use an NTC thermistor instead of a PTC one as intended. Theoretically this would allow the Thermoflagger to work in reverse and instead monitor extreme cold events. Since I have been doing some testing of circuits in chambers with TEC units, I can see this being particularly useful to detect when boards get under the dewpoint, allowing for monitoring when dangerous condensation could be occurring. As can be seen in the below graph, looking at the resistance curves for PTC and NTC, the chip should behave in reverse with an NTC element.
CONCLUSION
To answer my title question, “Useful or Gimmick,” I would say this little family of chips is useful. It’s actually quite surprising that something like this hasn’t been around for decades given how simple it really is. For the ease of use and extremely cheap price point it hits, there really is nothing bad to say about it. It removes the need for tying up an analog peripheral in a microcontroller and beats out nearly any other similar solution in nearly every category.
