3 Solutions

TI’s TMP61 is a positive temperature coefficient linear thermistor (PTC) provides high linearity and consistent sensitivity over the entire temperature range, realizing a simple and accurate method of temperature conversion. Various packages of the chip are suitable for different application scenarios, as shown in Figure 3-1.

Figure 3-1 TMP61 Packages

• TMP61 silicon-based thermistor good R-T linearity

  The TMP61 linear thermistor is made of silicon, and unlike the metals and their oxides used in NTCs, its resistance versus temperature is linear, so it has many advantages. Its R-T table is shown in Figure 3-2. In the air-conditioning system, a single type of TMP61 silicon-based thermistor can achieve temperature detection at different locations under the premise of high resolution, while simplifying material management.

  Figure 3-2 TMP61 R-T Relationship Diagram
• TMP61 silicon-based thermistor faster response time

  In the comparison experiment of the response speed of TMP61 silicon-based thermistor and NTC, it is found that the response time of TMP61 can be up to 3 times faster than that of NTC. The experimental results are shown in Figure 3-3. In air conditioning systems, TMP61 silicon-based thermistor is used for outdoor condense coil, which can improve the conditioning performance of condenser temperature control. Taking heating as an example, the rapid response and high accuracy of the defrosting control of the condenser can effectively shorten the working time of the air-conditioning compressor during defrosting and reduce the energy consumption of the system.

  Figure 3-3 Comparison of Response Speed Between TMP61 and NTC
• TMP61 silicon-based thermistor save ROM and simplifies software design

  The R-T table of silicon-based thermistor is almost linear, and the R-T relationship can be directly fitted. At the same time, TI also provides the Thermistor Design Tool, which includes R-T fitting relationship, low-pass filtering, oversampling and other functions, and provides the relevant code that can be used directly, as shown in Figure 3-4. Taking the sampling circuit of 20K pull-down resistor as an example, the output relationship between temperature and voltage of TMP61 is obtained as shown in Figure 3-5. The relationship between temperature and voltage is almost linear, and a linear function can be used to fit it.

  Figure 3-4 TMP61 Thermistor Design Tool
  Figure 3-5 The Output Relationship Diagram of Temperature and Voltage of TMP61

In addition to the advantages mentioned above, TMP61 silicon-based thermistor thermistors also have the advantages of small resistance tolerance, easy single point calibration and less drift. For more information, see Temperature Sensing with Thermistors.