a Low Cost, Current Output Temperature Transducer TMP17* FEATURES Operating Temperature Range: 2408C to 11058C Single Supply Operation: 14 V to 130 V Excellent Repeatability and Stability High Level Output: 1 mA/K Monolithic IC: Temperature In/Current Out Minimal Self-Heating Errors APPLICATIONS Appliance Temperature Sensor Automotive Temperature Measurement and Control HVAC System Monitoring Industrial Temperature Control Thermocouple Cold Junction Compensation FUNCTIONAL DIAGRAM NC NC V NC V NC NC NC PACKAGE DIAGRAM SO-8 NC 1 GENERAL DESCRIPTION V The TMP17 is a monolithic integrated circuit temperature transducer that provides an output current proportional to absolute temperature. For a wide range of supply voltages the transducer acts as a high impedance temperature dependent current source of 1 µA/K. Improved design and laser wafer trimming of the IC’s thin-film resistors allows the TMP17 to achieve absolute accuracy levels and nonlinearity errors previously unattainable at a comparable price. V The TMP17 can be employed in applications between 240°C to 1105°C where conventional temperature sensors (i.e., thermistor, RTD, thermocouple, diode) are currently being used. Expensive linearization circuitry, precision voltage references, bridge components, resistance measuring circuitry and cold junction compensation are not required with the TMP17. 7 NC TOP VIEW 3 (Not to Scale) 6 NC NC 4 5 NC NC = NO CONNECT The TMP17 is available in a low cost SO-8 surface-mount package. PRODUCT HIGHLIGHTS 1. A wide operating temperature range (240°C to 1105°C) and highly linear output make the TMP17 an ideal substitute for older, more limited sensor technologies (i.e., thermistors, RTDs, diodes, thermocouples). 2. The TMP17 is electrically rugged; supply irregularities and variations or reverse voltages up to 20 V will not damage the device. 3. Because the TMP17 is a temperature dependent current source, it is immune to voltage noise pickup and IR drops in the signal leads when used remotely. 378 4. The high output impedance of the TMP17 provides greater than 0.5°C/V rejection of supply voltage drift and ripple. IOUT – µA 343 5. Laser wafer trimming and temperature testing insures that TMP17 units are easily interchangeable. 1µA/K 273 248 45 8 NC 2 25 0 70 TEMPERATURE – C 105 125 6. Initial system accuracy will not degrade significantly over time. The TMP17 has proven long term performance and repeatability advantages inherent in integrated circuit design and construction. Figure 1. Transfer Characteristic * Protected by U.S. Patent No. 4,123,698 REV. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. © Analog Devices, Inc., 1996 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703 TMP17F/G–SPECIFICATIONS (V = 15.0 V, 2408C ≤ T ≤ 1058C, unless otherwise noted) S Parameter Symbol ACCURACY TMP17F TMP17G TMP17F TMP17G Power Supply Rejection Ratio 14 V < VS < 15 V 15 V < VS < 115 V 115 V < VS < 130 V Nonlinearity Conditions Min Typ TA = 125°C1 TA = 125°C1 Over Rated Temperature Over Rated Temperature Max Units 62.5 63.5 63.5 64.5 °C °C °C °C 0.5 0.3 0.3 Over Rated Temperature2 0.5 °C/V °C/V °C/V °C TA = 125°C (298.2K) Over Rated Temperature Note 3 TA = 1150°C for 500 Hrs4 298.2 1 0.2 0.2 µA µA/°C °C °C/month PSRR PSRR PSRR OUTPUT Nominal Current Output Scale Factor Repeatability Long Term Stability POWER SUPPLY Supply Range A 1VS 4 30 V NOTES 1 An external calibration trim can be used to zero the error @ 125°C. 2 Defined as the maximum deviation from a mathematically best fit line. 3 Maximum deviation between 125°C readings after a temperature cycle between 240°C and 1105°C. Errors of this type are noncumulative. 4 Operation at 1150°C. Errors of this type are noncumulative. Specifications subject to change without notice. METALIZATION DIAGRAM ABSOLUTE MAXIMUM RATINGS* Maximum Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . 130 V Operating Temperature Range . . . . . . . . . . 240°C to 1105°C Maximum Forward Voltage (1 to 2) . . . . . . . . . . . . . . 144 V Maximum Reverse Voltage (2 to 1) . . . . . . . . . . . . . . . 120 V Dice Junction Temperature . . . . . . . . . . . . . . . . . . . . . 1175°C Storage Temperature Range . . . . . . . . . . . . 265°C to 1160°C Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . 1300°C 62MILS V+ 37MILS V– NOTES *Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and functional operation at or above this specification is not implied. Exposure to the above maximum rating conditions for extended periods may affect device reliability. TEMPERATURE SCALE CONVERSION EQUATIONS 8C = 5 (8F 2 32) 9 8F = 9 8C 1 32 5 K = 8C 1 273.15 ORDERING GUIDE Model Max Cal Error @ +258C Max Error –408C to +1058C Nonlinearity –408C to +1058C Package Option TMP17FS TMP17GS 2.5°C 3.5°C 3.5°C 4.5°C 0.5°C 0.5°C SO-8 SO-8 CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the TMP17 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. –2– WARNING! ESD SENSITIVE DEVICE REV. 0 Typical Performance Characteristics–TMP17 1.0 6 5 V = ACCURACY WITHOUT TRIM MAX LIMIT 5V 0.5 TEMPERATURE ERROR – C 4 2 TOTAL ERROR – C 3 1 1 2 3 0 1 5 2 4 0 AFTER SINGLE TEMPERATURE CALIBRATION 0.5 1.0 3 4 MIN LIMIT 5 40 6 50 25 0 25 50 75 TEMPERATURE – C 100 25 125 25 TEMPERATURE – C 105 Figure 5. Long-Term Stability @ 1125 °C Figure 2. Accuracy vs. Temperature 500 100 450 CONSTANT IOUT UP TO 30V 90 V 5V SOIC PACKAGE SOLDERED TO 0.5" 0.3" Cu PCB 70 IOUT = 378µA 400 OUTPUT CURRENT – µA PERCENT OF CHANGE – % 80 = 60 50 40 30 350 300 IOUT = 298µA 250 TA = 105 C IOUT = 233µA 200 TA = 150 25 C 100 20 TA = 50 40 C 10 0 0 0 5 10 15 TIME – sec 20 25 30 0 1 2 3 4 SUPPLY VOLTAGE – V 5 Figure 6. V-I Characteristics Figure 3. Thermal Response in Stirred Oil Bath 60 TIME CONSTANT – sec 2µs TRANSITION FROM 100 C STIRRED BATH TO FORCED 25 C AIR V = 5V 50 100 90 SOIC PACKAGE SOLDERED TO 0.5" 0.3" Cu PCB 40 VIN = 0V to 5V RL = 1kΩ, TA = 25 C 30 20 10 0% 10 0 200mV 0 100 200 300 400 AIR VELOCITY – FPM 500 600 Figure 7. Output Turn-On Settling Time Figure 4. Thermal Time Constant in Forced Air REV. 0 –3– 6 TMP17 0.2 THEORY OF OPERATION The TMP17 uses a fundamental property of silicon transistors to realize its temperature proportional output. If two identical transistors are operated at a constant ratio of collector current densities, r, then the difference in base-emitter voltages will be (kT/q)(ln r). Since both k, Boltzmann’s constant, and q, the charge of an electron, are constant, the resulting voltage is directly Proportional To Absolute Temperature (PTAT). In the TMP17 this difference voltage is converted to a PTAT current by low temperature coefficient thin film resistors. This PTAT current is then used to force the total output current to be proportional to degrees Kelvin. The result is a current source with an output equal to a scale factor times the temperature (K) of the sensor. A typical V-I plot of the circuit at 125°C and the temperature extremes is shown in Figure 6. NONLINEARITY – C 0.1 TYPICAL NONLINEARITY 0 0.1 0.2 40 Factory trimming of the scale factor to 1 µA/K is accomplished at the wafer level by adjusting the TMP17’s temperature reading so it corresponds to the actual temperature. During laser trimming the IC is at a temperature within a few degrees of 125°C and is powered by a 5 V supply. The device is then packaged and automatically temperature tested to specification. 0 25 25 TEMPERATURE – C 70 105 Figure 8. Nonlinearity Error (TMP17) TRIMMING FOR HIGHER ACCURACY Calibration error at 125°C can be removed with a single temperature trim. Figure 9 shows how to adjust the TMP17’s scale factor in the basic voltage output circuit. FACTORS AFFECTING TMP17 SYSTEM PRECISION +V The accuracy limits given on the Specifications page for the TMP17 make it easy to apply in a variety of diverse applications. To calculate a total error budget in a given system it is important to correctly interpret the accuracy specifications, nonlinearity errors, the response of the circuit to supply voltage variations and the effect of the surrounding thermal environment. As with other electronic designs external component selection will have a major effect on accuracy. TMP17 R 100Ω VOUT = 1mV/K 950Ω CALIBRATION ERROR, ABSOLUTE ACCURACY AND NONLINEARITY SPECIFICATIONS Figure 9. Basic Voltage Output (Single Temperature Trim) Two primary limits of error are given for the TMP17 such that the correct grade for any given application can easily be chosen for the overall level of accuracy required. They are the calibration accuracy at 125°C, and the error over temperature from 240°C to 1105°C. These specifications correspond to the actual error the user would see if the current output of a TMP17 were converted to a voltage with a precision resistor. Note that the maximum error at room temperature or over an extended range, including the boiling point of water, can be directly read from the specifications table. The error limits are a combination of initial error, scale factor variation and nonlinearity deviation from the ideal 1 µA/K output. Figure 2 graphically depicts the guaranteed limits of accuracy for a TMP17GS. To trim the circuit the temperature must be measured by a reference sensor and the value of R should be adjusted so the output (VOUT) corresponds to 1 mV/K. Note that the trim procedure should be implemented as close as possible to the temperature highest accuracy is desired for. In most applications if a single temperature trim is desired it can be implemented where the TMP17 current-to-output voltage conversion takes place (e.g., output resistor, offset to an op amp). Figure 10 illustrates the effect on total error when using this technique. 1.0 ACCURACY WITHOUT TRIM 0.5 TOTAL ERROR – C The TMP17 has a highly linear output in comparison to older technology sensors (i.e., thermistors, RTDs and thermocouples), thus a nonlinearity error specification is separated from the absolute accuracy given over temperature. As a maximum deviation from a best-fit straight line this specification represents the only error that cannot be trimmed out. Figure 8 is a plot of typical TMP17 nonlinearity over the full rated temperature range. 0 AFTER SINGLE TEMPERATURE CALIBRATION 0.5 1.0 40 25 25 TEMPERATURE – C 105 Figure 10. Effect of Scale Factor Trim on Accuracy –4– REV. 0 TMP17 ment (θ JA). Self-heating error in °C can be derived by multiplying the power dissipation by θJA. Because errors of this type can vary widely for surroundings with different heat sinking capacities, it is necessary to specify θ JA under several conditions. Table I shows how the magnitude of self-heating error varies relative to the environment. In typical free air applications at 125°C with a 5 V supply the magnitude of the error is 0.2°C or less. A small glued-on heat sink will reduce the temperature error in high temperature, large supply voltage situations. If greater accuracy is desired, initial calibration and scale factor errors can be removed by using the TMP17 in the circuit of Figure 11. R2 5kΩ 97.6kΩ +5V R1 1kΩ 8.66kΩ OP196 REF43 VOUT = 100mV/oC 7.87kΩ TMP17 Table I. Thermal Characteristics V– Figure 11. Two Temperature Trim Circuit With the transducer at 0°C adjustment of R1 for a 0 V output nulls the initial calibration error and shifts the output from K to °C. Tweaking the gain of the circuit at an elevated temperature by adjusting R2 trims out scale factor error. The only error remaining over the temperature by adjusting R2 trims out scale factor error. The only error remaining over the temperature range being trimmed for its nonlinearity. A typical plot of two trim accuracy is given in Figure 12. τ (sec)* Still Air Moving Air @ 500 FPM Fluorinert Liquid 158 60 35 52 10 2 Response of the TMP17 output to abrupt changes in ambient temperature can be modeled by a single time constant τ exponential function. Figures 3 and 4 show typical response time plots for media of interest. The time constant, τ, is dependent on θJA and the thermal capacities of the chip and the package. Table I lists the effective τ (time to reach 63.2% of the final value) for several different media. Copper printed circuit board connections will sink or conduct heat directly through the TMP17’s soldered leads. When faster response is required a thermally conductive grease or glue between the TMP17 and the surface temperature being measured should be used. The power supply rejection characteristics of the TMP17 minimize errors due to voltage irregularity, ripple and noise. If a supply is used other than 5 V (used in factory trimming), the power supply error can be removed with a single temperature trim. The PTAT nature of the TMP17 will remain unchanged. The general insensitivity of the output allows the use of lower cost unregulated supplies and means that a series resistance of several hundred ohms (e.g., CMOS multiplexer, meter coil resistance) will not degrade the overall performance. MOUNTING CONSIDERATIONS If the TMP17 is thermally attached and properly protected, it can be used in any temperature measuring situation where the maximum range of temperatures encountered is between 240°C and 1105°C. Thermally conductive epoxy or glue is recommended under typical mounting conditions. In wet environments condensation at cold temperatures can cause leakage current related errors and should be avoided by sealing the device in nonconductive epoxy paint or conformal coating. 2.0 1.0 TOTAL ERROR – C θJA (8C/watt) NOTES *τ is an average of one time constant (63.2% of final value). In cases where the thermal response is not a simple exponential function, the actual thermal response may be better than indicated. SUPPLY VOLTAGE AND THERMAL ENVIRONMENT EFFECTS 0 APPLICATIONS 1.0 Connecting several TMP17 devices in parallel adds the currents through them and produces a reading proportional to the average temperature. Series TMP17s will indicate the lowest temperature because the coldest device limits the series current flowing through the sensors. Both of these circuits are depicted in Figure 13. 2.0 40 25 0 25 TEMPERATURE – C 75 105 Figure 12. Typical Two Trim Accuracy The thermal environment in which the TMP17 is used determines two performance traits: the effect of self-heating on accuracy and the response time of the sensor to rapid changes in temperature. In the first case, a rise in the IC junction temperature above the ambient temperature is a function of two variables; the power consumption level of the circuit and the thermal resistance between the chip and the ambient environREV. 0 Medium –5– TMP17 +15V +5V The circuit shown can be optimized for any ambient temperature range or thermocouple type by simply selecting the correct value for the scaling resistor – R. The TMP17 output (1 µA/K) times R should approximate the line best fit to the thermocouple curve (slope in V/°C) over the most likely ambient temperature range. Additionally, the output sensitivity can be chosen by selecting the resistors RG1 and R G2 for the desired noninverting gain. The offset adjustment shown simply references the TMP17 to °C. Note that the TC’s of the reference and the resistors are the primary contributors to error. Temperature rejection of 40 to 1 can be easily achieved using the above technique. TMP17 TMP17 TMP17 TMP17 333.3Ω (0.1%) VTAVG (1mV/K) 10kΩ (0.1%) VTAVG (10mV/K) Although the TMP17 offers a noise immune current output, it is not compatible with process control/industrial automation current loop standards. Figure 16 is an example of a temperature to 4–20 mA transmitter for use with 40 V, 1 kΩ systems. Figure 13. Average and Minimum Temperature Connections The circuit of Figure 14 demonstrates a method in which a voltage output can be derived in a differential temperature measurement. In this circuit the 1 µA/K output of the TMP17 is amplified to 1 mA/°C and offset so that 4 mA is equivalent to 17°C and 20 mA is equivalent to 33°C. Rt is trimmed for proper reading at an intermediate reference temperature. With a suitable choice of resistors, any temperature range within the operating limits of the TMP17 may be chosen. +V 10kΩ TMP17 OP196 +20V 5MΩ R1 50kΩ TMP17 VOUT = (T1 – T2) x 17 C ≈ 4mA 33 C ≈ 20µA REF01E (10mV/oC) 10kΩ 1mA/ C 35.7kΩ –V RT 10mV/ C TMP17 5kΩ OP97 Figure 14. Differential Measurements C R1 can be used to trim out the inherent offset between the two devices. By increasing the gain resistor (10 kΩ) temperature measurements can be made with higher resolution. If the magnitude of V1 and V2 is not the same, the difference in power consumption between the two devices can cause a differential self-heating error. +7.5V 2.5V REF43 MEASURING JUNCTION APPROX. R VALUE J K T E S R 52Ω 41Ω 41Ω 61Ω 6Ω 6Ω 10kΩ Cu 500Ω VT –20V Figure 16. Temperature to 4–20 mA Current Transmitter Reading temperature with a TMP17 in a microprocessor based system can be implemented with the circuit shown in Figure 17. +5V REF43 RGAIN ROFFSET 2.5V R RCAL C F ROFFSET RGAIN ≈ 9.1kΩ ≈ 9.8kΩ 100kΩ 180kΩ OP196 VOUT = 100mV/( C OR F) ROFFSET/RGAIN TMP17 OP193 1kΩ 5kΩ 12.7kΩ 10Ω Cold junction compensation (CJC) used in thermocouple signal conditioning can be implemented using a TMP17 in the circuit configuration of Figure 15. Expensive simulated ice baths or hard to trim, inaccurate bridge circuits are no longer required. THERMOCOUPLE TYPE 10kΩ VOUT V– TMP17 Cu REFERENCE JUNCTION 100kΩ RG2 (1kΩ) RG1 Figure 17. Temperature to Digital Output R By using a differential input A/D converter and choosing the current to voltage conversion resistor correctly, any range of temperatures (up to the 145°C span the TMP17 is rated for) centered at any point can be measured using a minimal number of components. In this configuration the system will resolve up to 1°C. Figure 15. Thermocouple Cold Junction Compensation –6– REV. 0 TMP17 A variable temperature controlling thermostat can easily be built using the TMP17 in the circuit of Figure 18. control which row of sensors are being measured. The maximum number of TMP17s which can be used is the product of the number of channels of the decoder and mux. +15V 10V An example circuit controlling 80 TMP17s is shown in Figure 20. A 7-bit digital word is all that is required to select one of the sensors. The enable input of the multiplexer turns all the sensors off for minimum dissipation while idling. REF01E RPULL-UP RHIGH 62.7kΩ TMP17 AD790 COMPARATOR RSET 10kΩ C ROW SELECT +15V RHYST 10kΩ COLUMN SELECT TEMP > SETPOINT OUTPUT HIGH RLOW 27.3kΩ TEMP < SETPOINT OUTPUT LOW 4028 BCD TO DECIMAL DECODER (OPTIONAL) VOUT AD7501 8-CHANNEL MUX C Figure 18. Variable Temperature Thermostat RHIGH and RLOW determine the limits of temperature controlled by the potentiometer RSET. The circuit shown operates over the temperature range 225°C to 1105°C. The reference maintains a constant set point voltage and insures that approximately 7 V appears across the sensor. If it is necessary to guardband for extraneous noise, hysteresis can be added by tying a resistor from the output to the ungrounded end of RLOW. +15V –15V EN 80 – TMP17s Multiple remote temperatures can be measured using several TMP17s with a CMOS multiplexer or a series of 5 V logic gates because of the device’s current-mode output and supply-voltage compliance range. The on-resistance of a FET switch or output impedance of a gate will not affect the accuracy, as long as 4 V is maintained across the transducer. Muxes and logic driving circuits should be chosen to minimize leakage current related errors. Figure 19 illustrates a locally controlled mux switching the signal current from several remote TMP17s. CMOS or TTL gates can also be used to switch the TMP17 supply voltages, with the multiplexed signal being transmitted over a single twisted pair to the load. +15V Figure 20. Matrix Multiplexer To convert the TMP17 output to °C or °F a single inexpensive reference and op amp can be used as shown in Figure 21. Although this circuit is similar to the two temperature trim circuit shown in Figure 11, two important differences exist. First, the gain resistor is fixed alleviating the need for an elevated temperature trim. Acceptable accuracy can be achieved by choosing an inexpensive resistor with the correct tolerance. Second, the TMP17 calibration error can be trimmed out at a known convenient temperature (i.e., room temperature) with a single pot adjustment. This step is independent of the gain selection. –15V VOUT T8 T2 T1 AD7501 REMOTE TMP17s D E C O D E R / S1 S2 S8 D R I V E R 10kΩ 10kΩ +5V REF43 RGAIN ROFFSET 2.5V R RCAL C F ROFFSET RGAIN ≈ 9.1kΩ ≈ 9.8kΩ 100kΩ 180kΩ OP196 VOUT = 100mV/(oC OR oF) ROFFSET/RGAIN TMP17 TTL DTL TO CMOS I/O V– EN CHANNEL SELECT Figure 21. Celsius or Fahrenheit Thermometer Figure 19. Remote Temperature Multiplexing To minimize the number of muxes required when a large number of TMP17s are being used, the circuit can be configured in a matrix. That is, a decoder can be used to switch the supply voltage to a column of TMP17s while a mux is used to REV. 0 –7– TMP17 OUTLINE DIMENSIONS Dimensions shown in inches and (mm). C2154–8–7/96 8-Lead Narrow-Body SOIC (SO-8) 0.1968 (5.00) 0.1890 (4.80) PIN 1 0.0098 (0.25) 0.0040 (0.10) SEATING PLANE 8 5 1 4 0.2440 (6.20) 0.2284 (5.80) 0.0688 (1.75) 0.0532 (1.35) 0.0500 0.0192 (0.49) (1.27) 0.0138 (0.35) BSC 0.0196 (0.50) x 45° 0.0099 (0.25) 0.0098 (0.25) 0.0075 (0.19) 8° 0° 0.0500 (1.27) 0.0160 (0.41) PRINTED IN U.S.A. 0.1574 (4.00) 0.1497 (3.80) –8– REV. 0