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Table of Contents

User’s Guide

NTC Thermistor to TMP6 Linear Thermistor Replacement
Guide

ABSTRACT
Linear thermistors use the same hardware and software design methods commonly used with linear positive
temperature coefficient or negative temperature coefficient thermistors. The purpose of this document is toprovide insight on hardware and software design methods for converting a NTC thermistor system to a linear
thermistor.

Table of Contents
1 Introduction.............................................................................................................................................................................2
1.1 NTC Thermistor Versus TMP6 Linear Thermistor Family.................................................................................................. 2
1.2 NTC/Linear Thermistor TCR.............................................................................................................................................. 2
1.3 NTC Versus Silicon-Based Linear Thermistor Trade-Offs..................................................................................................2
1.4 TMP6 Accuracy..................................................................................................................................................................5
2 Typical NTC Thermistor Design Considerations................................................................................................................. 6
2.1 Voltage-Biased NTC Thermistor Network.......................................................................................................................... 6
2.2 Pinouts/Polarity.................................................................................................................................................................. 7
2.3 Converting NTC Thermistor Hardware Design to TMP6 Linear Thermistor Design.......................................................... 7
2.4 Simple Look-Up Table........................................................................................................................................................ 9
3 Software Changes.................................................................................................................................................................13
3.1 Firmware Design Considerations..................................................................................................................................... 13
3.2 Oversampling................................................................................................................................................................... 15
3.3 Low-Pass Filtering in HW Versus SW.............................................................................................................................. 17
3.4 Calibration........................................................................................................................................................................ 21
4 Design considerations for Full-Scale Range Voltage Output........................................................................................... 23
4.1 Simple Current-Biased..................................................................................................................................................... 23
4.2 Active Voltage-Biased...................................................................................................................................................... 24
5 Conclusion............................................................................................................................................................................ 26
6 Additional Resources/Considerations................................................................................................................................27
6.1 Constant-Current Source Design..................................................................................................................................... 27
6.2 TMP6 Thermistor Standard Component Footprints......................................................................................................... 27
6.3 Dual-Sourcing Approach for TMP6 and NTC Thermistors...............................................................................................28

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1 Introduction
Thermistors can be used in temperature sensing applications instead of digital temperature sensors due to their
reduced cost, lower footprint, and faster response time. More information on the benefits of thermistors overdigital temperature sensors can be found in Temperature Sensing using Thermistors.

1.1 NTC Thermistor Versus TMP6 Linear Thermistor Family
The two main thermistors in the market are the NTC and linear thermistors. NTC thermistors operate bychanging the resistance as temperature increases or decreases. Linear thermistors change their effective
resistance while a current is flowing through them, depending on the temperature. The largest difference
between the two types is that NTC thermistor's resistance will decrease logarithmically while a linear thermistor's
effective resistance will increase linearly as the temperature increases. The graph below shows the difference inresistance to temperature characteristics of a typical 10-kΩ NTC thermistor versus TI's TMP6 Linear Thermistor
family, specifically the TMP6131 DEC package.

Figure 1-1. RT Curve of Typical NTC Thermistor vs. TMP6131DEC Thermistor

1.2 NTC/Linear Thermistor TCR
The temperature coefficient resistance (TCR) can be defined as the change in resistance as temperaturechanges for a device. Use Equation 1 to calculate the TCR measured in ppm/°C.
Temperature Characteristic Resistance = ((R2–R1)/R1×(T2–T1))×10^6(1)

Due to the linearity of the TMP61 thermistor, the device has a consistent TCR across a wide operating
temperature range. Unlike an NTC thermistor, which is a purely resistive device, the TMP61 thermistor's
effective resistance is affected by the current across the device and the effective resistance changes when
the temperature changes. The TMP61 thermistor has a 6400 ppm/°C TCR (25°C) with a 0.2% typical TCR
tolerance across the entire temperature range. However, this value does vary slightly depending on how the
TMP61 thermistor is biased.
The TMP6 thermistor has many advantages while the NTC thermistor, at first glance, has an advantage ofchange in resistance at room temperature. The TMP6 thermistor can achieve the same or better accuracy withsimple enhancements that TI provides.

1.3 NTC Versus Silicon-Based Linear Thermistor Trade-Offs
The configuration of the temperature sensing circuit in one's design will depend on any number of factors. Whilevoltage-biased thermistors are simpler to construct, current-biased thermistors have a wider dynamic voltage
range, greater stability, and higher accuracy across the temperature range for the output voltage VTEMP.

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Introduction

The typical NTC thermistor has a tolerance range from (1% to 5%) between temp extremes, although this canbe higher for some NTC thermistors, while the TMP61 thermistor has a tolerance of (0.5% to 1.5%) between
extremes [–40°C, +150°C] which can be seen in Figure 1-2 below.

Figure 1-2. Resistance Tolerance of Typical NTC Thermistor vs. TMP6 Linear Thermistor
The thermistor's greatest strength is its simplicity in design. With a voltage-biased or current-biased network,
a voltage drop across the thermistor or a current can be passed through the thermistor to be measured forsensing. The main configurations for a thermistor circuit are voltage-biased, as demonstrated in the voltage
divider configuration in Figure 1-3, or current-biased, as shown in Figure 1-4. The output voltage, VTEMP, can be
fed to an ADC for digital processing of the temperature data in the MCU.

VBIAS
VREF

VREF
IBIAS

RBIAS
VTEMP

VTEMP

XOUT

t0

t0

GND

GND

/

/

PTC / NTC

PTC / NTC

GND

GND

Figure 1-3. Thermistor Voltage Divider Circuit

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XOUT
ADC

ADC

Figure 1-4. Thermistor Current Source Circuit

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When looking at the characteristics of an NTC thermistor, it should be noted that when the ambient temperature
is hot, the NTC thermistor presents a challenge to see what the temperature is at due to the low sensitivity
at these higher temperatures. For easier software processing of incoming temperature data, one might needto linearize their NTC thermistor's R-T table. For NTC thermistors, this typically requires a fixed resistancevalue in parallel with the thermistor. Figure 1-5 shows a typical NTC thermistor voltage divider circuit witha parallel resistor of RP and a bias resistor RBIAS. A comparison of the voltage response of a typical NTC
thermistor voltage divider, typical linear thermistor voltage divider and NTC thermistor voltage divider withparallel resistance is shown in Figure 1-6.
+VBIAS+VBIAS

RBIAS

VTEMP
ADC

RP

NTC

GND
GND

Figure 1-5. NTC Thermistor With Parallel Resistor
5
VNTC
VTMP61VNTC with RP

VTEMP (V)

4

3

2

1

0
-60

-40

-20

0

20 40 60 80
Temperature (qC)

100 120 140 160
d012

Figure 1-6. NTC Thermistor With and Without a Linearization Resistor vs. TMP61 Thermistor Temperature
Voltages
Thiscan work for a limited temperature range, but it is more difficult to linearize an NTC thermistor over the entire
temperature range and cannot be done with hardware only. Conversely, linear thermistors are fabricated witha linear R-T characteristic curve, which eliminates the requirement for a fixed-value resistor in parallel with thethermistor.
System designers may require a calibration on thermistors to ensure accuracy across the operating range ofthe device. To achieve higher accuracy across this range, NTC thermistors require multiple-point calibration at
different temperature values such as -40°C, 25°C, and 125°C due to the non-linearity of an NTC thermistor. The
same theory can be applied to a linear thermistor, but because of the linearity, only a single-point calibration (at25°C, for example) is needed. Therefore, using a linear thermistor will save on manufacturing time and reduce
memory demands on the MCU for temperature processing. Refer to the Thermistor Design Tool for additional
information on calibration with the TMP6 linear thermistor family of devices.

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Introduction

1.4 TMP6 Accuracy
Following the design steps included in the document while taking various designs including Rbias tolerance/
PPM, Temperature Range of interest, Polynomial/LUT, Oversampling, Filtering and Calibration into account , thefollowing table summarizes the accuracy in °C that can be achieved with the TMP6 linear thermistor.

Figure 1-7. TMP6 Thermistor Accuracy in °C
The accuracy numbers in the chart include assumptions of an ideal Vbias at 5 V and an ideal Vref with no ADC
error.

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2 Typical NTC Thermistor Design Considerations
Let us follow an example of this design process:
Table 2-1. System Requirements for Example Voltage-Biased Temperature Sensing Circuit
Temperature Range

Bias Voltage

TMIN

TMAX

VBIAS

-40 C

125 C

5V

2.1 Voltage-Biased NTC Thermistor Network
The simplest construction of the NTC thermistor-based temperature sensing network is the one shown in Figure2-1. For the ADC, we will use 12-bit resolution and a reference voltage of 5 VDC. The 12-bit resolution is anacceptable resolution for measurement while the 5 VDC reference voltage simplifies power rail requirements.
These design decisions result in the voltage response shown in Figure 2-2.
+VBIAS+VBIAS

RBIAS

VTEMP
ADC

NTC

GND
GND

Figure 2-1. Simple Voltage Biased NTC Thermistor Schematic

Figure 2-2. NTC Thermistor Voltage Response (5 V)
While this voltage-biased network is very simple, reducing the bill of materials cost required. The temperature
output VTEMP shows non-linear behavior at the temperature extremes.
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Typical NTC Thermistor Design Considerations

2.2 Pinouts/Polarity
The TMP6 linear thermistor is a 2-pin device and therefore a pin-to-pin replacement of an NTC thermistor. These
devices are also footprint-compatible as the TMP6 thermistor is offered in 0402 (1005-mm) and 0603 (1608-mm)
packages. It should be noted that the 0603 part can also be used on an 0805 footprint. See Section 6.2 for more
information.
It is important to note that the TMP6 thermistor has polarity (see Figure 2-3).
ID Area

±

1

2

+

Figure 2-3. TMP6 Thermistor DYA Package 2-Pin SOT-5X3 Bottom View (Angled)
TI uses a special silicon process where the doping level and active region areas devices control the key
characteristics (the TCR and nominal resistance). The device has an active area and a substrate due to thepolarized terminals. Connect the positive terminal to the highest voltage potential and the negative terminal
to the lowest voltage potential to ensure proper operation. If the voltage across the pads is reversed, thethermistor will appear properly until the p-n junction starts to conduct (approximately 0.6 V), then the thermistor
I-V characteristics will break down. This will result in a measurement of 0.6 V across the device terminals if
configured reversely.

2.3 Converting NTC Thermistor Hardware Design to TMP6 Linear Thermistor Design
For a simple NTC thermistor design, the converting from an NTC thermistor to the TMP6 Linear Thermistor is
straightforward. The only hardware change is to swap the NTC thermistor and the TMP61 thermistor, while RBIAS
can be left as is. The resulting transformation can be seen in Figure 2-4 below.

Figure 2-4. TMP6 Linear Thermistor Voltage Divider Circuit

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The circuit above results in the following voltage response. Notice how the voltage response is positive.

Figure 2-5. TMP6 Linear Thermistor Positive Voltage Response
A positive voltage response can be used for new designs, but matching a negative response that the original
NTC thermistor circuit generated may be useful for old designs. To provide a negative voltage response with the
TMP6 Linear Thermistor, the bias resistor and TMP6 Linear Thermistor must switch positions. After redesigning,
you can see the resulting negative voltage response below.
+VBIAS+VBIAS

PTC

VTEMP
ADC
RBIAS

GND

GND

Figure 2-6. TMP6 Linear Thermistor Circuit for Negative Voltage Response

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Typical NTC Thermistor Design Considerations

Figure 2-7. TMP6 Linear Thermistor Negative Voltage Response

2.4 Simple Look-Up Table
Now that we have the hardware design completed, the TI thermistor design tool can be used to generate
software for internal resistance-temperature conversion within the MCU. Take a look at how to generate the codesnippets from the Thermistor Design Tool.
We will use the following design parameters:
5-V, 10-kΩ bias resistor, 12-bit ADC, TMP6131DYA.

Figure 2-8. Thermistor Design Tool Parameters

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Next we can move to the Device Resistance Tables tab. Here we can find both a 1°C and 5°C step look-up table.
This page dynamically populates the resistance tables depending on the design parameters initially set. The 5°C
Look-Up Table is shown below:

Figure 2-9. 5°C LUT

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On this page, we can find C code for the look-up table, as well.

Figure 2-10. 5°C LUT C CodeSBOU246 – JANUARY 2022
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From simply implementing a look-up table, a comparison between the TMP6 thermistor accuracy and a typical
NTC thermistor across the full operating temperature range is plotted below.

Figure 2-11. Un-Corrected Thermistor Accuracy Comparison

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Software Changes

3 Software Changes
When the output of the thermistor circuit is sensed by an ADC and converted to digital information for the
MCU to process, the output must be converted to a temperature value. One of the common software R-T
conversion methods is using a look-up table. This involves pre-populating a table of resistances and theassociated temperature value for those resistances. The code will determine which resistance value moreclosely aligns with the expected temperature value by interpolating between the points. This method results in avery simple setup for the R-T table but puts high demand on the flash memory requirements for the MCU and alengthy array-parsing program. It can also be inaccurate due to system errors such as tolerance variations andtemperature coefficients which may lead to divergence from the ideal R-T table.
A second method of temperature conversion that can save on memory is the Steinhart-Hart equation below. The
equation can be implemented into the temperature sensing code for mapping to the R-T curve of the thermistor:
1/T = A + B × ln(R) + C × ln3(R)(2)

where T = temperature (in Kelvin); R = measured resistance value; A,B,C are the calculated coefficients.
With the use of the TMP6 linear thermistor, however, a much better algorithm is available for converting is the
4th order polynomial regression model below:
T = A4 × R4 + A3 × R3 + A2 × R2 + A1 × R + A0

(3)

where T = temperature (in Celsius); R = measured resistance value; A0-4 are the calculated polynomial
coefficients.
This approximation works well because of the linearity of the device and does not work for a non-linear NTC
thermistor. The polynomial coefficients for the polynomial regression model can be generated in the Thermistor
Design Tool.

3.1 Firmware Design Considerations
The recommended method for calculating the temperature values from TI's TMP6 Linear Thermistor portfolio is
the 4th order polynomial regression. This is the most accurate and fastest method to calculate the temperaturewith no look-up table needed. Moving on to the 4th Order Polynomial TMP vs. Res tab, we find both the

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Quartic Function and Regression model which provide the 4th order polynomial for the calculated temperature/
resistance of the device.

Figure 3-1. 4th Order Polynomial
Here we provide the C code that can be readily implemented into a system designers software to calculate thetemperature of the TI TMP6 linear thermistor chosen.

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Software Changes

Figure 3-2. 4th Order Polynomial C Code

3.2 Oversampling
Oversampling and averaging temperature measurements in a first-in-first-out (FIFO) sequence can improvemeasurement resolution and signal-to-noise ratio. This is recommended when using less than a 12-bit ADC,
although it can applied to 12-bit or 14-bit ADCs, as well. After the ADC reads the bit value and your code
calculates the temperature, you can store that value in an array. As a new value comes into the array, theoldest sample is dropped as all the other samples are shifted to the next corresponding cell, thus creating a
FIFO. The averaging method can be applied to any of the values used in temperature conversion such as thetemperature, the ADC bit value, the divider voltage, or even the calculated resistance. For every 8 oversamples
the resolution will increase by 2 bits. 16 oversamples will increase a 10-bit ADC to 14 bits of resolution. The
figures below demonstrate two methods on how the oversampling can be implemented. See the Averaging tabof the Thermistor Design Tool for more information.

Figure 3-3. Oversampling Method 1

Figure 3-4. Oversampling Method 2

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An example of the C code for Method 1 provided from the Thermistor Design Tool can be seen in Figure 3-5.

Figure 3-5. Oversampling Example C Code16

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Figure 3-6 and Figure 3-7 below you can see the impact of filtering the TMP6331 Thermistor's raw data using as
12-bit ADC. After a 32x oversample, the data aligns with the reference probe more closely.

Figure 3-6. TMP6331 Thermistor Data With No Oversampling

Figure 3-7. TMP6331 Thermistor Data With 32x Oversampling Applied

3.3 Low-Pass Filtering in HW Versus SW
Noise can cause erroneous temperature measurements, which is why many designers choose to add an RC
filter in hardware to filter out noise coming from the system. But instead of filtering in hardware, you can use
this method to eliminate the need for the extra resistor and capacitor, enabling greater board and cost savings.
Implementing your filter in software gives you more control over the filter's response by changing the alpha value
in real time. Additionally, having the ability to set the filtered temperature minimizes your start-up time.
There are three variables needed for the firmware based low-pass filter:
1. Alpha
2. Measure Temp
3. Filtered Temp

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Alpha: This variable controls how much noise is filtered out.
Measured Temp: This variable stores your calculated, pre-filtered temperature reading.
Filtered Temp: This variable stores the resulting temperature after having passed the temperature value throughthe filter.
The firmware low-pass filtering is executed by the following equation:
Low pass filter equation:
Y n = 1−α ×Y n−1 + α×X n

(4)

where
• Y = Filtered Temp
• α = Alpha• X = Measured Temp
Simplifying...

Y n =Y n−1 − α× Y n−1 −X n(5)

Simplifying further...

Y n =Y− α× Y−X
Meas_Temp))

meaning Filtered_Temp = Previous_Filtered_Temp - (Alpha * (Previous_Filtered_Temp -On the Low-Pass Filter tab of the Thermistor Design Tool, you can adjust the alpha and samples per second
values to change the filter. In Figure 3-8, you can see that the alpha was set to 0.8. The result seen in Figure 3-9
is that the resulting temperature data after implementing the low pass filter does not change much from the raw
data.

Figure 3-8. Low-Pass Filter Setting With 0.8 Alpha Value

Figure 3-9. Low-Pass Filter Response With 0.8 Alpha Value18

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After adjusting the alpha value, a filtered response for an alpha value of 0.2 is shown below:

Figure 3-10. Low-Pass Filter Response With 0.2 Alpha Value
Here you can see that the filtered temperature data comes out to be much smoother than the raw data.
An example of the C code for the low pass filter from the Thermistor Design Tool can be seen in Figure 3-11.

Figure 3-11. Low-Pass Filter Example C CodeSBOU246 – JANUARY 2022
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After oversampling and implementing the low-pass filter algorithm the TMP6 thermistor can show improved
performance. A comparison between the corrected TMP6 thermistor and a typical NTC thermistor can be shown
below:

Figure 3-12. Corrected Thermistor Accuracy Comparison
See the Low-Pass Filter tab of the Thermistor Design Tool for more information.

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3.4 Calibration
Figure 3-13 shows the accuracy across the temperature range of multiple TMP6 thermistor units. As can beseen in the figure, each units accuracy varies, but shows linearity. Thanks to the high linearity of the TMP6x
thermistors and their similarity across units, we can remove the tolerance errors from the thermistor, VCC, VREF,
ADC LSB and bias resistor and get a very consistent accuracy across the whole temperature range without
additional costs. You will need a high accuracy temperature reference. The TMP117 is a high-accuracy, lowpower, digital temperature sensor with a NIST traceable accuracy of ±0.3°C (maximum) from –55°C to +150°C.
You will need to add some amount of automation to the process after the firmware has been programmed into
the UUT (Unit Under Test). After adding in the calibration, the units are now lined up within ±0.3°C across thetemperature range (see Figure 3-14).

Figure 3-13. TMP6 Thermistor Potential Temperature Error

Figure 3-14. TMP6 Thermistor Potential Temperature Error With Correction
Process: The production programming device will program the firmware into the UUT. Once the UUT powers up
for the first time, the UUT will use its ADC to measure the VSensevoltage from the TMP6x thermistor on the
PCB, calculate the temperature, and write the temperature into the temperature register. At this point either the
production programming device or the UUT will read the temperature register in the UUT and read the external
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temperature reference, subtract the measured temperature from the external temperature reference, and write
this value into the offset register. For all future temperature measurements the UUT will add the measured TMP6
thermistor temperature value to the offset register value for the final corrected temperature.
Assumptions: The UUT and temperature reference is at ambient temperature. The UUT will be operating at
low power during firmware programming. The TMP6x thermistor's temperature will be measured immediately
upon power up. The offset will be calculated based on the first temperature measured upon power up and thetemperature reference.
After implementing a single point calibration, a comparison between the accuracy of an NTC thermistor and the
TMP61 Linear Thermistor is shown in Figure 3-15.

Figure 3-15. Offset Corrected Total Thermistor Temperature Error Compared

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Design considerations for Full-Scale Range Voltage Output

4 Design considerations for Full-Scale Range Voltage Output
While the voltage divider circuit with the TMP61 thermistor is simple to convert to, it does not take advantage ofthe full-scale range of the ADC input. There are two recommended design approaches to increase the full scale
range of the thermistor divider circuit. One approach is to use a current source and the other is to design yourcircuit with the addition of an operation amplifier. The following sections will help to design these circuits.

4.1 Simple Current-Biased
A superior configuration of the TMP61 linear thermistor is to use a current-biased network. Similar to the design
steps above, the simplest model for a current-biased TMP61 linear thermistor network is the one shown in
Figure 4-1 below. For the ADC, we will use 12-bit resolution and a reference voltage VBIAS of 5 V.
+VBIAS

IBIAS

VTEMP
ADC

TMP61

GND

GND

Figure 4-1. TMP6 Linear Thermistor Current Source Circuit
With an ADC reference voltage of 5 V, using a 200-µA current source to bias the TMP61 thermistor is a good
option. The resulting Vtemp voltage swing from -40°C to 125°C is 1.3226 V to 3.58 V as shown in the simulation
below.

Figure 4-2. TMP61 Thermistor Voltage Swing With 200-µA Current Source

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Varying the current when implemented with the TMP61 thermistor will increase the dynamic range of the output
response. When biasing the TMP61 thermistor with currents between 50 µA and 400 µA, the output responses
can be shown below:
9
IBIAS = 50 PA
IBIAS = 100 PA
IBIAS = 200 PA
IBIAS = 300 PA
IBIAS = 400 PA

8
7

VTEMP (V)

6
5
4
3
2
1
0
-60

-40

-20

0

20 40 60 80
Temperature (qC)

100 120 140 160
d013

Figure 4-3. TMP61 Thermistor Temperature Voltage With Varying Current Sources
The proper value of the bias current is dependent on the reference voltage of the ADC in your system. You will
want to choose the value so that the dynamic range is optimized with the full-scale range of the ADC input. In
most cases, 200 µA is recommended. For lower system current draw a TI TMP6 linear thermistor of a higher
nominal resistance such as the TMP64 (47 kΩ) and TMP63 (100 kΩ) thermistors can be used. The best current
source implementation for the TMP64 (47 kΩ) and TMP63 (100 kΩ) thermistors are 42.533 µA and 20 µA,
respectively.

4.2 Active Voltage-Biased
The hardware change for the active thermistor network involves a few more steps. Similar to the simple design
above, the first hardware change is to swap the NTC and TMP61 thermistors, while RBIAS can remain as is.
+VBIAS+VBIAS+VBIAS

R2
R3
RBIAS
R1

VTEMP

GND

–
ADC
+

PTC

TMP61

GND

GND

Figure 4-4. TMP6 Linear Thermistor Schematic With Op Amp
Following the design steps of the guide, we end up with resistance values of RBIAS = 10 kΩ, R1 = 6.84 kΩ, R2= 6.25 kΩ and R3 = 10 kΩ. The resulting V_OUT has range of 0.129 V to 4.86 V, which is within the linear

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Design considerations for Full-Scale Range Voltage Output

operating range of the op amp and provides better resolution. These design decisions result in the voltage
response shown in Figure 4-5 below.

Figure 4-5. TMP6 Linear Thermistor With Op Amp Voltage Response

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5 Conclusion
In conclusion, when comparing an NTC thermistor and a linear thermistor, an NTC thermistor may seem to havea benefit of resolution around room temperature. However, when we take a deeper look we can see that there
are many added benefits to using a linear thermistor, such as TI's TMP61 linear thermistor family, rather thanan NTC thermistor. Switching out the component of an NTC thermistor and TI's TMP61 linear thermistor can bedone due to the parts being a pin to pin replacement. When considerations of oversampling, low pass filtering,calibration are also put in to place a much higher accuracy over the entire temperature range can be achieved
with TI's TMP6 family of thermistors.

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Additional Resources/Considerations

6 Additional Resources/Considerations
6.1 Constant-Current Source Design
Using the TI thermistor design tool, we can design a constant-current source appropriate for temperaturesensing with thermistors.

Figure 6-1. Constant Current Source Design
The TLV9062 is a dual-channel operation amplifier with rail-to-rail input and output-swing capabilities.
Spice models for the TMP6131 thermistor can be found on the product folder here.

6.2 TMP6 Thermistor Standard Component Footprints
The TMP6 thermistors are currently available in a X1SON (DEC), SOT-5X3 (DYA) and TO-92S (LPG) packages.
The DYA package sits on an IPC-782A 0603 footprint with no issues to fit or solder quality. TI recommends toreduce the pads if possible to minimize excess copper to achieve the maximum sensitivity of the part. However
it’s not necessary to change the foot print at all. The size of the footprint has no bearing on the accuracy of the

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Additional Resources/Considerations

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part. Also note that the IPC recommends increasing the land pad size to increase robustness in wave soldering.
This is good for this device when using a standard 0603 pad size.

Figure 6-2. TMP6 DYA Package on IPC-782A 0603 Footprint
While the data sheet highlights the SOT-5X3/DYA package being 0603/1608 footprint-compatible, it is also
compatible with the 0805/2012 footprint due to its unique lead frame dimensions.

Figure 6-3. TMP6 Thermistor DYA on IPC-782A-0805 Footprint
When the DYA, IPC 0603 and IPC 0805 PCB footprints are overlaid, as shown in image below, it can beseen that the recommended PCB foot print for the DYA has a slightly larger space recommendation than the0603/1608 or the 0805/2012. The important part to observe in this comparison is to ensure the heel of the
TMP6 thermistor pins, as landed on the 0805/2012 pads will allow for the required heel fillet according to
the IPC-A-610G standards (for solder quality). The toe and side fillets will easily meet the same IPC-A-610G
requirements with the larger pad size that the 0805/2012 footprint presents as compared to either the 0603/1608
or the DYA footprint.
Additional details can be found on the e2e forum in the TMP61 Thermistor FAQ here.

6.3 Dual-Sourcing Approach for TMP6 and NTC Thermistors
A common system requirement is the ability to multi-source components on a BOM. This section provides amethod for multi-sourcing with the TMP6 and an NTC thermistors. The key adjective here is to determine which
device is onboard based on its initial change in voltage (∆V ) to use the correct temperature conversion codefrom then on.

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The first step is to pre-determine the direction of the initial change in temperature (∆T) during start-up. Duringassembly, the board can heat up by about 5°C on its own due to self heating of power supplies, the processor,
etc. If you'd like, you can induce a greater change in temperature by using a heat lamp (+∆T) or freeze spray(-∆T ).
The second step is to have your software determine if the initial change in voltage (∆V ) during start-up is
positive (+) or negative (-). Using the table below as a reference, your software can determine which thermistor
type is onboard and use the correct temperature conversion code.

Figure 6-4. Dual Sourcing for TMP6 and NTC Thermistors

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