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Power consumption is under 12μA with 10μA of that going through the thermistor as sensing current. Lower current (<2μA) versions are planned.
Inside is a current source to feed the PTC and a reference voltage with which the returning voltage of the PTC is compared.
This are not a precision ICs (numbers below), and rely on the sharply-non-linear rising resistance characteristics of PTC thermistors.
This sharp characteristic allows a single IC to be used with a number of PTC thermistors connected in series (diagram left), with the rapid transition from low to high resistance in any one of them tripping the IC – allowing over-temperature detection in ‘n’ places with n thermistors and one IC.
The trip level is nominally 500mV with 100mV hysteresis. This can vary over 420 to 580mV at 25°C, or 360 to 640mV over a -40 to 125°C junction range. It is recommended that the IC is not mounted next to the sensed temperatures.
Nominal sense current varies, for example in 1μA versions, with: manufacture, (0.92 – 1.08μA, 25°C, Vcc=3.3V), supply voltage (0.80 – 1.22μA over the 1.7 – 5.5V operating range) and temperature (0.76 – 1.27μA, -40 to 125°C, 3.3V).
Options across the family, called TCTH0xxxE and branded ‘Thermoflagger’, are: latching or non-latching output, totem pole or open drain output, and 10μA or 1μA thermistor sense current – eight devices are planned to cover all the options.
Latching versions have a reset input (RESET) to clear the latch, while in non-latching versions, this pad is labelled ground (GND2) instead, about which Electronics Weekly enquired as v1.0 of the data sheet was not clear.
It transpires that this is a pad that needs to be grounded, not a second ground pad.
“TCTH0x1 [non-latching] series are using the same circuit design as TCTH0x2 [latching] series,” Toshiba told Electronics Weekly. “There is a reset function in the [non-latching] TCTH0x1, but it is not used as reset function. When GND2 is open or high level, the device may malfunction, so GND2 need to be on a low level the same as GND1.”
The first two devices available are both 10μA sense open-drain types: TCTH021BE is non-latching and TCTH022BE is latching.
All come in a 1.6 x 1.6 x 0.55mm SOT-553 package.
Industrial applications are also foreseen.
