The new linear 10 kΩ silicon thermistors TMP61, TMP63 and TMP64 from Texas Instruments have an unusually high stability with a tolerance of ±1% and achieve up to 50% higher accuracy compared to classic NTC thermistors. High sensitivity and one-point calibration are further advantages. This makes it possible to push the thermal limits of the other components and the system as a whole even further during operation. In addition to maximizing performance, component complexity and thus solution costs can be reduced.
Although NTC thermistors are very common due to their low price, they prove to be problematic for circuit developers in various ways. For example, the performance of thermistors degrades at temperature extremes due to their negative temperature coefficient. Due to the complex calibration requirements, the development effort is greater.
The new TMP61, TMP63 and TMP 64 PTC linear thermistors from Texas Instruments, which have been in the manufacturer's portfolio since the beginning of the year, are offered at similar prices to NTC thermistors, but offer significantly greater benefits (Fig. 1). In particular, they minimize the time required for design, reduce component costs and increase system performance [1]. A detailed data sheet for the use of TPM61 can be found at [2].
Special manufacturing process
The three linear silicon thermistors have a linear positive temperature coefficient (PTC), which results in a uniform and consistent temperature coefficient resistance (TCR) over a wide operating temperature range. TI uses a special silicon process in which the doping levels and regions of the active areas in the component control the key properties (temperature coefficient resistance TCR and nominal resistance R25). The component has an active area and a substrate due to the polarized connections.
Advantages for system performance and reliability
Especially at temperatures above 80 °C, the new thermistors from TI provide reliable and highly accurate temperature measurements. This is particularly important in industrial, automotive and consumer applications where precise real-time temperature readings are critical to system performance and protection. An 8-page white paper entitled 'Temperature Sensing with Termistors', published by TI in January 2020 and available via [3], looks at the more precise differences between NTCs and TI's linear thermistors.
Due to their low sensitivity and high resistance tolerance at extreme temperatures, NTC thermistors lead to less accurate temperature readings. To counteract these problems, many developers carry out calibrations at three points in the temperature range or use several thermistors to monitor different temperature ranges. However, even these methods can produce unreliable temperature readings, meaning that systems may have to be shut down before their true thermal limits are reached. In contrast, the linearity and high accuracy of TI thermistors allow for single-point calibration, which maximizes system performance and simplifies design.
TI thermistors are also characterized by a very low thermal drift of 0.5%, which improves the reliability of temperature measurements and allows designers to increase system performance while ensuring safe operation. Designers can use TI's thermistor design tool, which is referenced on TI's thermistor product pages and datasheets, to quickly and easily calculate temperature-resistance values [2].
Two further basic parameters:
- Temperature range -40°C to +125°C
- Fast thermal response time of 0.6 s (DEC)
Reduced system costs, less space required
By eliminating the need for additional linearization circuitry or redundant NTC thermistors, TI's thermistors help designers simplify their designs, reduce system costs and reduce the size of the PCB layout by at least 33% compared to NTC thermistors (Fig. 2). Last but not least, TI thermistors are only a tenth of the size of comparable silicon-based linear thermistors. Their flat design and small housing footprint allows them to be placed closer to thermal hot spots, which results in shorter response times and more consistent temperature measurements (Table 1). Figure 3 shows the functional diagram.
| Enclosure type | Base dimensions (nominal) |
| X1SON (2) | 0.60 × 1.00 mm |
| TO-92S (2) | 1.52 × 3.15 mm |
| SOT-5×3 (2) | 0.80 × 1.20 mm |
Tab. 1: Dimensions of the housing base of TMP61 [2]
Fig. 3: Functional diagrams of TMP61Availability and prices
TI's new thermistor portfolio with the TMP61, TMP63 and TMP64 devices is now available from authorized distributors at prices starting at $0.05 (1000 pieces or more).
The TMP61 is currently available in a 0402 footprint-compatible X1SON package, a 0603 footprint-compatible SOT-5X3 package and a 2-pin TO-92S through-hole package.
References:
[1] www.ti.com/thermistors-pr
[2] www.ti.com/lit/ds/symlink/tmp61.pdf
[3] www.ti.com/lit/wp/slay054/slay054.pdf
