NTC Thermistors Summary Issue date: April 2011 • All specifications are subject to change without notice. • Conformity to RoHS Directive: This means that, in conformity with EU Directive 2002/95/EC, lead, cadmium, mercury, hexavalent chromium, and specific bromine-based flame retardants, PBB and PBDE, have not been used, except for exempted applications. (1/4) NTC Thermistors Summary FEATURES TDK NTC thermistors are high-quality thermistors that have been manufactured from carefully selected high-quality materials. TDK uses unique fine ceramics manufacturing and precision machining to manufacture its high quality thermistors. • Small, compact, and highly responsive to temperature changes. • Tightly controlled B constant for predictable and accurate temperature measurement. • Highly reliable. • The chip type, the glass diode type, and the resin coated type are prepared according to the applications. Moreover, it is possible to correspond widely as an assembly product which makes the best use of these features. APPLICATIONS TDK NTC thermistors are widely used as the followings. Field Applications Intake-air temperature sensors, exhaust-air temperature sensors, cooling-water temperature sensors, lubricating-oil temperature sensors Oil fan heaters, solar heating systems, air conditioners Automobile Air conditioning Office automation equipment Medical instruments Cooking appliances Home medical electronics Household appliances Information and Telecommunications Copier-facsimiles, computer equipment Clinical thermometers, intravenous injection temperature regulators, neonatal incubators Microwave ovens, steam ovens, electric crock pots, electric ranges, electric ovens Electronic clinical thermometers, warm washing toilets, electric curling irons Refrigerators, irons, electric water-heaters, electric tea-pots, electric coffee-makers, washing machines, TVs, video cassette recorders, stereo sets, radios Cellular phones, chargeable battery pack, personal computers PHYSICAL PROPERTIES OF NTC THERMISTORS INITIAL RESISTANCE Thermistor resistance is a function of absolute temperature as indicated by the following relationship: 1 1 ............................................................ (1) – R=R0 • expB T T0 ( ) Here R0, R(kΩ) are the respective resistance values when the surrounding temperature is T0, T(K). B is the thermistor constant(B constant below). B CONSTANT The B constant is found from the following equation: B= 2.3026(logR–logR0) 1 – 1 T T0 .......................................................(2) This B characteristic is indicated by the slope of the linear plot of log R-1/T inverse absolute temperature. The B constant value is generally in the vicinity of 2500K to 5000K. B constant values of 3000K to 4000K are frequently used for measurements. Resistance-temperature characteristics (Fig.1) 450 400 350 300 Temperature(˚C) 250 200 150 100 100 20kΩ /200˚C 10 Resistance (kΩ) NTC(Negative Temperature Coefficient) Thermistors are manufactured from sintered metal oxides. Each thermistor consists of a combination of two to four of the following materials: Manganese, Nickel, Cobalt and Copper. These semiconductor resistors exhibit decreasing resistance characteristics with increasing temperature, and have a low thermal time constant resulting in an extremely high rate of resistance change to accurately track the temperature. Conformity to RoHS Directive 3.3kΩ/100˚C 1 1.4 1.6 1.8 2 2.2 1 × 10 3 (K) T 2.4 2.6 2.8 3 TEMPERATURE COEFFICIENT The relationship between temperature coefficient α and B becomes: B 1 dR α= • = – 2 ×100(%/°C) ..............................................(3) T R dT The negative sign of the temperature coefficient indicates that the temperature coefficient decreases as both thermistor resistance and temperature rise. If B is taken as 3400K, the temperature coefficient found at 20°C (293.15K) becomes –4%/°C. HEAT DISSIPATION COEFFICIENT Temperature rises due to thermal energy formed as electrical current flows through the thermistor. The thermistor temperature T0 is then related to the surrounding temperature Ta and the electrical input W: W=k(T0–Ta)=V•I(mW) ............................................................(4) k= W (mW/°C) ...............................................................(5) T0 –Ta This k value is the heat dissipation coefficient, which represents the additional electrical power (mW/°C) needed to raise the thermistor temperature by 1°C. This heat dissipation coefficient varies with changes in the measurement and environmental conditions. When a thermistor is used for temperature measurement, it is naturally important to lower the applied electrical current as much as possible in order to reduce measurement error resulting from self heating. • Conformity to RoHS Directive: This means that, in conformity with EU Directive 2002/95/EC, lead, cadmium, mercury, hexavalent chromium, and specific bromine-based flame retardants, PBB and PBDE, have not been used, except for exempted applications. • All specifications are subject to change without notice. 004-04 / 20110428 / eb221_ntc_sum.fm (2/4) VOLTAGE - CURRENT CHARACTERISTIC The voltage - current characteristic indicates the drop in voltage as electrical current through the thermistor is gradually increased. Voltage-current characteristics (Fig.2) 100 5 4 10 3 Voltage (V) 2 1 1 0.1 Ta=25˚C (in still air) No.1 5kΩ 2 10kΩ 3 20kΩ 4 50kΩ 5 100kΩ 10 100 1 Current (mA) HEATING TIME CONSTANT The time period required to heat up a thermistor from a certain temperature T0 over a target temperature rise is called the heating time constant. Various types of heating time constants are indicated by the symbols shown in Table 1 as determined by the percent change from T0 toward the target temperature. The standard change is typically taken to be 63.2%. Thermal time constants (Fig.3) 70 Heating Th 40 Tc 30 20 (T0 –Ta) ×0.368 Temperature (˚C) 50 T0 (T0 –Ta) ×0.632 60 Room temperature Ta Cooling 10 0 τ 2τ 3τ 4τ 5τ 6τ 7τ Table 1 Heating time constant and temperature change ratio Code τ 2τ 3τ 4τ 5τ 6τ 7τ Rate of change (%) for T0 -Ta 63.2 86.5 95.0 98.2 99.4 99.8 99.9 • All specifications are subject to change without notice. 004-04 / 20110428 / eb221_ntc_sum.fm (3/4) PRODUCT IDENTIFICATION NTC D S 3H G 202 J C 3 (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) • Chip type: Please refer to the NTCG Series catalog (eb221_ntcg). • Assembled products: Please refer to the NTCGP/NTCDP Series catalog (eb225_ntcdp). (1) This code denotes NTC thermistors. (6) Nominal resistance This code indicates the resistance value existing at the specified ambient temperature by two significant digits followed by the digit 0(zero). (Example) (2) Structural classification code D G Glass sealed diode shape Multilayer element (3) Assembly classification code S C E D A B Z 470Ω 5kΩ 10kΩ 150kΩ Without processing Short cut lead wire Kinked lead wire Kinked lead wire with insulation tube Folded radial lead wire Folded radial lead wire with insulation tube Others (7) Nominal resistance tolerance Tolerance is identified by the following codes. (4) B constant(Resistance temperature characteristics) This code indicates the value of B constant using a combination of one numeric and one alphabetic character. Numeric code 1 2 3 4 5 B constant(K) 1000 2000 3000 4000 5000 Alphabetic code A B C D E F Note: Although B constants are G expressed as 1A, 1B, 2A, 2B, etc. H using these two tables, the alphabetic characters do not denote J tolerances;they have the meaning K shown in the example below. L M (Example) N 1A=1000(K) P 1A=1050(K) That is, the alphabetic character(in Q this example, A) indicates the range R of values that can be specified by the S thermistor user. T U V B constant(K) 0 to 50 51 to 100 101 to 150 151 to 200 201 to 250 251 to 300 301 to 350 351 to 400 401 to 450 451 to 500 501 to 550 551 to 600 601 to 650 651 to 700 701 to 750 751 to 800 801 to 850 851 to 900 901 to 950 951 to 999 (5) B constant tolerance This code indicates tolerances using the following code. Code F G H J K 471 502 103 154 Tolerance(%) ±1 ±2 ±3 ±5 ±10 Code F G H J Tolerance(%) ±1 ±2 ±3 ±5 (8) Ambient temperature for nominal resistance Ambient temperatures for specified nominal-resistance values are indicated using the following codes. Code A B C D E F G X Ambient temperature(°C) –20 0 25 100 200 300 20 Others (9) Dimensional code 3 4 5 3018(3.0×ø1.8mm) 4020(4.0×ø2.0mm) Resin dip shape (10) Plating specification code of lead wire N S Ni Sn (11) Packaging style B T K Bulk Taping(Tape width: 52mm) Taping(Tape width: 26mm) (12) TDK internal code • All specifications are subject to change without notice. 004-04 / 20110428 / eb221_ntc_sum.fm (4/4) PERFORMANCE AND TEST METHODS ELECTRICAL CHARACTERISTICS Item Resistance value B constant Heat dissipation constant Thermal time constant Withstand voltage Rated power Test method Measure the value at a power level such that the influences of spontaneous heat generation can be negligible at the specified ambient temperature. Using the following expression, calculate the value from the resistances at the two specified ambient temperatures. B=2.3026 Specifications The measured values must stay within the specified limits. The measured values must stay within the specified limits. (logR – logR2) 1 1 – T T0 This constant denotes the power level(mW/°C) that is needed to increase the thermistor temperature by 1°C. It is calculated by the energy consumption at any two temperatures and previously measured resistance-temperature characteristic values using the following expression. W (mW/°C) k= T0– Ta The measured values must stay within the specified limits. Abruptly change the ambient temperature of the thermistor and measure the time until it reaches 63.2%(1τ) of the temperature difference. Apply the specified voltage to the electrically insulated section of the thermistor under the specified conditions. Measure the maximum power level at which any increment in thermistor temperature stays within 0.2°C due to spontaneous heat generation. The measured values must stay within the specified limits. No abnormalities must occur. The measured values must stay within the specified limits. MECHANICL CHARACTERISTICS Item Tensile strength of terminal Bending strength of terminal Test method Secure the thermistor body, and then apply a tensile force to it under the specified conditions and maintain this state for the specified time. Secure the thermistor body and then apply loads to it under the specified conditions. Repeat this procedure the specified number of times. Vibration resistance Apply vibration under the specified conditions. Repeat this procedure the specified times. Shock resistance Apply shock under the specified conditions. Repeat this operation the specified number of times. Solderability Solder the thermistor terminals under the specified conditions and check their solderability. Resistance to soldering heat Apply a thermal soldering shock to the thermistor under the specified conditions, then leave the thermistor in a standard state for the specified time(one hour or more), before measurement. Specifications Damage must not occur. Damage must not occur. Measured values must stay within the specified limits. Measured values must stay within the specified limits. Measured values must exceed the specified limits. Measured values must stay within the specified limits. ENVIRONMENTAL TESTS Item Low temperature storage High temperature storage Heat cycle Heat shock Moisture resistance High temperature loading Test method Allow the thermistor to stand in air at the minimum permissible operating temperature for the specified time. Place and maintain the thermistor in a normal condition for one hour or more before measurements. Allow the thermistor to stand in air at the maximum permissible operating temperature for the specified time. Place and maintain the thermistor in a normal condition for one hour or more before measurements. Cycle the thermistor at the minimum permissible operating temperature, the maximum permissible operating temperature, and room temperature for the specified time. Repeat this cycle for the specified number of times. Subsequently, place and maintain the thermistor in a normal condition for one hour or more before measurements. Cycle the thermistor at the minimum permissible operating temperature and the maximum operating temperature for the specified time respectively. Repeat this cycle for the specified number of times. Subsequently, place and maintain the thermistor in a normal condition for one hour or more before measurements. Allow the thermistor to stand in air at the specified temperature and relative humidity for the specified times. Subsequently, place and maintain the thermistor in a normal condition for one hour or more before measurements. Apply the specified electrical load to the thermistor at the maximum permissible operating temperature for the specified time. After that, place and maintain the thermistor in a normal condition for one hour or more before measurements. Specifications Measured values must stay within the specified limits. Measured values must stay within the specified limits. Measured values must stay within the specified limits. Measured values must stay within the specified limits. Measured values must stay within the specified limits. Measured values must stay within the specified limits. • The test conditions and the specified values are decided individually. • All specifications are subject to change without notice. 004-04 / 20110428 / eb221_ntc_sum.fm