How accurate is the detected temperature?

Depending on the combination of Thermoflagger™ and the PTC thermistor used , there may be variations in the detected temperature.

For reference, Table-1 shows the simulation results of the overheat detection temperature using the TCTH02xxE and Murata Manufacturing's PTC thermistor (POSISTOR), PRF18BC471QB5RB.

Table-1 Overheat detection temperature-simulation for TCTH02xxE and PRF18BC471QB5RB
    Ambient temperature (Ta)
    25ºC 50ºC 85ºC
    Min Typ. Max Min Typ. Max Min Typ. Max
Conected PTC
thermistor quantity
(pcs)		 1 111ºC 120ºC 131ºC 110ºC 120ºC 134ºC 110ºC 120ºC 134ºC
5 111ºC 120ºC 131ºC 110ºC 120ºC 133ºC 109ºC 120ºC 134ºC
10 110ºC 120ºC 131ºC 109ºC 120ºC 133ºC 107ºC 119ºC 133ºC
15 110ºC 119ºC 131ºC 108ºC 119ºC 133ºC 104ºC 118ºC 133ºC
Fig. 1 Causes of Detected Temperature Variation
Fig. 1 Causes of Detected Temperature Variation

The variation in the detection temperature depends on VDET, IPTCO variation of Thermoflagger™, the resistance variation of the PTC thermistor, the number of connected PTC thermistors, and the ambient temperature. Before using this device, it is recommended to thoroughly verify it in an actual operating environment.

Fig. 2 Simulation Schematic
Fig. 2 Simulation Schematic

As an example, the following shows a simulated result when TCTH02xxE and PRF18BC471QB5RB 10 are combined at ambient (Ta) of 85°C. The combined temperature is 119ºC with a tolerance +14ºC/-12ºC.

Fig. 3 Simulation Results
Fig. 3 Simulation Results

For more information, refer to the application notebook, " Circuit proposal using Thermoflagger™ TCTH0 series and PTC thermistors ".

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