When faced with thousands of thermistor types, selection may cause considerable difficulties. In this technical article, I will introduce you to some important parameters to keep in mind when choosing a thermistor, especially when you want to use two commonly used thermistor types for temperature sensing (negative temperature coefficient NTC thermistor) Resistor or silicon-based linear thermistor). NTC thermistors are widely used because of their low price, but they provide low accuracy at extreme temperatures.

1. How to choose the right thermistor for the temperature sensor
When faced with thousands of thermistor types, selection may cause
considerable difficulties. In this technical article, I will
introduce you to some important parameters to keep in mind when
choosing a thermistor, especially when you want to use two commonly
used thermistor types for temperature sensing (negative temperature
coefficient NTC thermistor) Resistor or silicon-based linear
thermistor). NTC thermistors are widely used because of their low
price, but they provide low accuracy at extreme temperatures.
Silicon-based linear thermistors can provide better performance and
higher accuracy in a wider temperature range, but usually their price
is higher. In the following we will introduce that other linear
thermistors in the market can provide more cost-effective high-
performance options to help solve a wide range of temperature sensing
needs without increasing the overall cost of the solution.
The thermistor suitable for your application will depend on many
parameters, such as:
· BOM cost.
· Resistance tolerance.
· Calibration points.
· Sensitivity (change in resistance per degree Celsius).
· Self-heating and sensor drift.
BOM cost
The thermistor itself is not expensive. Because they are discrete,
their voltage drop can be changed by using additional circuits. For
example, if you are using a non-linear NTC thermistor and you want a
linear voltage drop across the device, you can choose to add
additional resistors to help achieve this feature. However, another
alternative that can reduce the total cost of the BOM and solution is
to use a linear thermistor that provides the required voltage drop.
The good news is that with our new linear thermistor series, these
two. This means that engineers can simplify the design, reduce system
costs and reduce the printed circuit board (PCB) layout size by at
least 33%.
Resistance tolerance

2. Thermistors are classified according to their resistance tolerance at
25 ° C, but this does not completely explain how they change with
temperature. You can use the minimum, typical, and maximum resistance
values provided in the design tool or device resistance and
temperature (R-T) tables in the data sheet to calculate the tolerance
for the relevant specific temperature range.
To illustrate how the tolerance varies with the thermistor
technology, let's compare NTC and our TMP61-based silicon-based
thermistor, which have a nominal resistance tolerance of ± 1%.
Calibration point
It is not known that the thermistor's position within its resistance
tolerance will reduce system performance because you need a larger
error range. Calibration will tell you the expected resistance value,
which can help you to greatly reduce the error range. However, this
is an additional step in the manufacturing process, so the
calibration should be kept as low as possible.
The number of calibration points depends on the type of thermistor
used and the temperature range of the application. For narrow
temperature ranges, one calibration point is suitable for most
thermistors. For applications that require a wide temperature range,
you have two options: 1) use NTC calibration three times (this is due
to their low sensitivity at extreme temperatures and high resistance
tolerance), or 2) use silicon-based linear thermal The resistance is
calibrated once, which is more stable than NTC.
Sensitivity
When trying to obtain good accuracy from a thermistor, a large change
in resistance (sensitivity) per degree Celsius is just one of the
problems. However, unless you obtain the correct resistance value in
the software by calibrating or selecting a thermistor with a low
resistance tolerance, a larger sensitivity will not help.
Because the NTC resistance value decreases exponentially, it has
extremely high sensitivity at low temperatures, but as the
temperature increases, the sensitivity will drop sharply. The
sensitivity of a silicon-based linear thermistor is not as high as
that of NTC, so it can perform stable measurements over the entire
temperature range. As the temperature increases, the sensitivity of a
silicon-based linear thermistor usually exceeds the sensitivity of
NTC at about 60 ° C.

3. Self-heating and sensor drift
The thermistor dissipates energy in the form of heat, which affects
its measurement accuracy. The amount of heat dissipated depends on
many parameters, including the material composition and the current
flowing through the device.
Sensor drift is the amount of thermistor drift over time, and usually
the accelerated life test given by the percentage change in
resistance value is specified in the data sheet. If your application
requires a long service life and consistent sensitivity and accuracy,
choose a thermistor with low self-heating and small sensor drift.
So, when should you use a silicon linear thermistor like TMP61 on
NTC?
Looking at Table 1, you can find that at the same price, silicon-
based linear thermistors can benefit from their linearity and
stability in almost any situation within the specified operating
temperature range of silicon-based linear thermistors. Silicon-based
linear thermistors are also available in commercial and automotive
versions, and are available in surface mount device NTC general
standard 0402 and 0603 packages.
parameter NTC thermistor Silicon-based linear
thermistor
BOM cost Low to medium:
.Low cost of
thermistor
.May require
additional
linearization circuit
Low：
.Low cost of
thermistor
.No additional
linearization circuit
required
Resistance tolerance Big:
Great difference
between tolerance and
extreme temperature
at 25 degrees
Small:
.within the entire
temperature range, a
small plus or minus
1.5%
.Maximum tolerance
Sensitivity Inconsistent: Consistent:

4. .Very large at low
temperatures
.Drops sharply as the
temperature rises
.Stable sensitivity
over the entire
temperature range
.NTC higher than
usually over 60
degrees
Standard point More:
.Wide application
requires multiple
points
one point:
.Only one point for
wide application
Self-heating and
sensor drift
high:
.Power consumption
increases with
temperature
.Large sensor drift
Minimum:
.Reduce power
consumption with
temperature
.Low sensor drift
Table 1: NTC and TI silicon-based linear thermistors
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