Temperature detector needs only 11.3μA

Temperature detector needs only 11.3μA

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.

Temperature detector needs only 11.3μA

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 to clear the latch, while non-latching versions get a second ground pad instead.

The first two devices 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.

The TCTH0xxxE family data sheet can be found here (Rev 1.0 of the data sheet may have errors adjacent to the GND2 connections on two of the diagrams on page 4)

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