TI Team,
I need clarification on the acceptable values allowed for NTC devices. As you know, the equation to compute RT2 is dependent on the thermistor cold and hot values. Here's what my problem is:
I've setup my TS resistor network using a thermistor from TKS. The NTC Thermistor is TSM type and the full part number is TSM0A103F34D1RZ-KB080415 (see attached pdf file). This thermistor that has a different temperature characteristic compare to the 103AT device found in the datasheet. The main difference is that the cold resistance on the battery thermistor (RTHcold) is about half of the (RTHcold) found in the example circuit on page 25; therefore, calculating the value of RT2 results in a negative value. The temperature range I would like the TS network to operate at is 15C-50C (see attached spreadsheet for calculations).
I haven't explored all possible values of thermistor values, but it seems that temperature range cannot exceed a certain ratio (between high and low), otherwise the value calculated in negative. The datasheet is not clear about what thermistor values are acceptable, nor does it explain if a ratio between the high and low values must be sustained.
I need to know if this thermistor will work in my design. I also would like to understand the range of thermistor values that are acceptable. I downloaded the software and a similar problem occurs when I don't use a specified range of thermistor values. Instead of getting a negative value for RT2, the software simply tells me that, "the temperature delta had to be increased for the device/sensor combination to work." Here's the link to the calculator. http://www.ti.com/tool/tempsense-sw
Thank you very much for your help, and I look forward to your response.
-David
