Surface Mount Thermistors-KR/TR/STC Series

RTI manufactures precision resistance-temperature SMD thermistors. Standard values from 250 ohms to 150,000 ohms are available. As with RTI’s disc and chip thermistors, SMD thermistors are suitable for temperature sensing applications over a wide range of resistance values and temperature coefficients. SMD’s operating temperature range is from -55°C to +150°C. Dissipation constant is 2mW/°C, with a maximum power rating of 250mW @ 25°C.

Applications

Most semiconductors and the circuits comprised of them exhibit a positive temperature coefficient. NTC thermistors are well suited for compensating these responses to temperature changes. It is important to match the temperature of the compensating NTC thermistor to that of the component responsible for the temperature response.

RTI’s SMD temperature measurement NTC sensors can operate over a wide temperature range (-55 to +150°C). They are stable throughout a long lifetime, and are small and comparatively inexpensive. Typically, they have negative temperature coefficients between -3.3 and -4.7%/°C at 25°C. RTI’s SMD style thermistors are used in many applications that require a high degree of accuracy and reliability.

Selection Considerations for SMD NTC Devices

• To determine the nominal resistance value of a thermistor at a specified temperature, multiply its RT/R25 value for the desired temperature and R-T curve from the table on NTC Resistance/Temperature Conversion Tables by its nominal resistance value at 25°C. As an example, the nominal resistance value at 80°C for a thermistor with the part number KR0805B103K is 10,000 times 0.157, the RT/R25 value in the R-T Curve “B” in the table under NTC Resistance/Temperature Conversion Tables.

• Standard resistance tolerances at 25°C for RTI’s SMD thermistors is ±10% and is indicated in its part number by the addition of the suffix K. To determine the resistance value at other than 25°C, add the appropriate DEV value from the NTC resistance/Temperature Conversion Tables to its resistance tolerance at 25°C. For example, the resistance tolerance at 80°C for a thermistor with part number KR0805B103K is ±10% ±3.0%, the DEV value from the R-T Curve “B” Table.

• Although standard sizes, resistance values and tolerances are listed on SMD Standard Products and Sizes, custom sizes, resistance values and tolerances are available depending on the application and volume requirements.

Consideration Notes:

• Calculate the DEV for R@T
• Review Power Dissipation
• Determine Required Accuracy
• Review Power Dissipation
• Select Required Resistance Values & Temperature Coefficient

KR SERIES

Configuration Options:

KR Series Size Chart

Size	0805		1206
Units	Inches	Millimeters	Inches	Millimeters
W	0.049 ±0.008	1.240 ±0.200	0.063 ±0.008	1.600 ±0.200
H	0.051 Maximum	1.300 Maximum	0.059 Maximum	1.500 Maximum
L	0.079 ±0.008	2.000 ±0.200	0.126 ±0.008	3.200 ±0.200
B	0.008 Minimum	0.200 Minimum	0.008 Minimum	0.200 Minimum

KR Series Product Chart

Part Number Size 0805	Part Number Size 1206	Resistance @ 25°C ±10% (Ohms)	Temperature Coefficient (@25°C)
KR0805A251K	KR1206A251K	250	-3.3%/°C
KR0805A501K	KR1206A501K	500	-3.3%/°C
KR0805J102K	KR1206J102K	1.0K	-3.5%/°C
KR0805J252K	KR1206J252K	2.5K	-3.5%/°C
KR0805B502K	KR1206B502K	5.0K	-3.9%/°C
KR0805B103K	KR1206B103K	10K	-3.9%/°C
KR0805C203K	KR1206C203K	20K	-4.4%/°C
KR0805C253K	KR1206C253K	25K	-4.4%/°C
KR0805C503K	KR1206C503K	50K	-4.4%/°C
KR0805W104K	KR1206W104K	100K	-4.7%/°C
KR0805W154K	KR1206W154K	150K	-4.7%/°C

KR Series Ordering Information

TR Size Chart

Size	0603		0805
Units	Inches	Millimeters	Inches	Millimeters
Length	0.063  ±0.006	1.60  ±0.150	0.080  ±0.008	2.00  ±0.20
Width	0.0315  ±0.006	0.80  ±0.15	0.050  ±0.004	1.25  ±0.10
Height	0.020  ±0.004	0.50  ±0.10	0.020  ±0.004	0.50  ±0.10
Termination	0.0012  ±0.0079	0.30  ±0.2	0.0016  ±0.008	0.40  ±0.20

TR Standard Product Chart

Part Number  Size 0603	Part Number  Size 0805	Resistance @ 25 °C ± 10%	Temp. Coefficient @ 25 °C
TR0603A251K	TR0805A251K	250	-3.3%/°C
TR0603A501K	TR0805A501K	500	-3.3%/°C
TR0603J102K	TR0805J102K	1.0K	-3.5%/°C
TR0603J252K	TR0805J252K	2.5K	-3.5%/°C
TR0603B502K	TR0805B502K	5.0K	-3.9%/°C
TR0603B103K	TR0805B103K	10K	-3.9%/°C
TR0603C203K	TR0805C203K	20K	-4.4%/°C
TR0603C253K	TR0805C253K	25K	-4.4%/°C
TR0603C503K	TR0805C503K	50K	-4.4%/°C
TR0603W104K	TR0805W104K	100K	-4.7%/°C
TR0603W154K	TR0805W154K	150K	-4.7%/°C

TR Series Ordering Information

TR = Model    0805 = Size   A = R-T Curve   251 =  *Resistance   K = **Tolerance   X = ***Termination

*Resistance value: First two digits are resistance value, third is the number of zeroes. Example: 251 = 250 ohms. 

** Tolerances available: K =±;10% and J=±;5%. 

***Terminations: No letter = Nickel Barrier (Consult factory for optional terminations). For tape and reel add suffix -T/R

 

TERMINOLOGY FOR SMD TEMPERATURE MEASUREMENT

• D.C. – The dissipation constant is the ratio, normally expressed in milliwatts per degree C (mw/°C), at a specified ambient temperature, of a change in power dissipated in a thermistor to the resultant change in body temperature.
• T.C. – The thermal time constant is the time required for a thermistor to change 63.2% of the total difference between its initial and final body temperature when subjected to a step function change in temperature under zero-power conditions and is normally expressed in seconds (S).
• Alpha (ß) or Temperature Coefficient of Resistance- The temperature coefficient of resistance is the ratio at a specified temperature, T, of the rate of change of zero-power resistance with temperature to the zero-power resistance of the thermistor. The temperature coefficient is commonly expressed in percent per degree C (%/°C).

 

R-T Curve	A	B	C	J	W
Temperature Coefficient @ 25°C	-3.3%/°C	-3.9%/°C	-4.4%/°C	-3.5%/°C	-4.7%/°C
Beta, ß	3000°K	3530°K	3965°K	3200°K	4250°K
R0°C/R50°C	5.3±5%	6.9±3%	9.1±3%	5.9±5%	10.45±5%
R25°C/R125°C	13.0	19.8	29.4	15.2	38.0