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FEATURES Operating Temperature Range: 40 C to 105 C Single Supply Operation: 4 V to 30 V Excellent Repeatability and Stability High Level Output: 1 A/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 GENERAL DESCRIPTION
Low Cost, Current Output Temperature Transducer TMP17*
FUNCTIONAL DIAGRAM
NC V V NC NC NC NC NC
PACKAGE DIAGRAM
SO-8
NC 1 V V 2 8 NC
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 A/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. The TMP17 can be employed in applications between 40C to 105C 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 5 NC
NC 4
NC = NO CONNECT
The TMP17 is available in a low cost SO-8 surface-mount package.
PRODUCT HIGHLIGHTS
1. A wide operating temperature range ( 40C to 105C) 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. 4. The high output impedance of the TMP17 provides greater than 0.5C/V rejection of supply voltage drift and ripple.
378
343 IOUT - A
1A/K
5. Laser wafer trimming and temperature testing insures that TMP17 units are easily interchangeable. 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.
273 248 45 25 0 70 TEMPERATURE - C 105 125
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. (c) 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 =
S
5.0 V,
40 C TA 105 C, unless otherwise noted)
Min Typ Max 2.5 3.5 3.5 4.5 0.5 0.3 0.3 Units C C C C C/V C/V C/V C A A/C C C/month 30 V
Parameter ACCURACY TMP17F TMP17G TMP17F TMP17G Power Supply Rejection Ratio 4 V < VS < 5 V 5 V < VS < 15 V 15 V < VS < 30 V Nonlinearity OUTPUT Nominal Current Output Scale Factor Repeatability Long Term Stability POWER SUPPLY Supply Range
Symbol
Conditions TA = 25C1 TA = 25C1 Over Rated Temperature Over Rated Temperature
PSRR PSRR PSRR Over Rated Temperature2 TA = 25C (298.2K) Over Rated Temperature Note 3 TA = 150C for 500 Hrs4 VS 4 0.5 298.2 1 0.2 0.2
NOTES 1 An external calibration trim can be used to zero the error @ 25C. 2 Defined as the maximum deviation from a mathematically best fit line. 3 Maximum deviation between 25C readings after a temperature cycle between 4 Operation at 150C. Errors of this type are noncumulative. Specifications subject to change without notice.
40C and
105C. Errors of this type are noncumulative.
ABSOLUTE MAXIMUM RATINGS*
METALIZATION DIAGRAM
Maximum Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . Operating Temperature Range . . . . . . . . . . 40C to Maximum Forward Voltage ( to ) . . . . . . . . . . . . . . Maximum Reverse Voltage ( to ) . . . . . . . . . . . . . . . Dice Junction Temperature . . . . . . . . . . . . . . . . . . . . . Storage Temperature Range . . . . . . . . . . . . 65C to Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . .
NOTES
30 V 105C 44 V 20 V 175C 160C 300C
62MILS V+
37MILS V-
*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
C= 5( F 9
32)
F= 9 C 5
32
K= C
273.15 ORDERING GUIDE
Model TMP17FS TMP17GS
Max Cal Error @ +25 C 2.5C 3.5C
Max Error -40 C to +105 C 3.5C 4.5C
Nonlinearity -40 C to +105 C 0.5C 0.5C
Package Option 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.
WARNING!
ESD SENSITIVE DEVICE
-2-
REV. 0
Typical Performance Characteristics-TMP17
1.0
6 5 V 4 TEMPERATURE ERROR - C
TOTAL ERROR - C
=
5V
MAX LIMIT
0.5
ACCURACY WITHOUT TRIM
3 2 1 0 1 2 3 4 5 6 50 25 0 MIN LIMIT 5 4 1 2 3
0 AFTER SINGLE TEMPERATURE CALIBRATION
0.5
1.0
40
25
25 50 75 TEMPERATURE - C
100
125
25 TEMPERATURE - C
105
Figure 2. Accuracy vs. Temperature
Figure 5. Long-Term Stability @ 125C
500 100 450 90 V 80 PERCENT OF CHANGE - % 70 60 50 40 30 20 50 10 0 0 0 5 10 15 TIME - sec 20 25 30 0 1 2 3 4 SUPPLY VOLTAGE - V 5 6 = 5V OUTPUT CURRENT - A 400 350 300 250 TA = 200 150 100 TA = 40 C TA = 25 C 105 C IOUT = 298A IOUT = 233A SOIC PACKAGE SOLDERED TO 0.5" 0.3" Cu PCB CONSTANT IOUT UP TO 30V IOUT = 378A
Figure 3. Thermal Response in Stirred Oil Bath
Figure 6. V-I Characteristics
60 TRANSITION FROM 100 C STIRRED BATH TO FORCED 25 C AIR V = 5V SOIC PACKAGE SOLDERED TO 0.5" 0.3" Cu PCB
2s
100 90
50 TIME CONSTANT - sec
40
VIN = 0V to 5V RL = 1k, TA = 25 C
30
20
10 0%
10
200mV
0
0
100
200 300 400 AIR VELOCITY - FPM
500
600
Figure 4. Thermal Time Constant in Forced Air
Figure 7. Output Turn-On Settling Time
REV. 0
-3-
TMP17
THEORY OF OPERATION
0.2
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 125C and the temperature extremes is shown in Figure 6. Factory trimming of the scale factor to 1 A/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 25C and is powered by a 5 V supply. The device is then packaged and automatically temperature tested to specification.
FACTORS AFFECTING TMP17 SYSTEM PRECISION
0.1 NONLINEARITY - C
TYPICAL NONLINEARITY
0
0.1
0.2
40
25
0
25 TEMPERATURE - C
70
105
Figure 8. Nonlinearity Error (TMP17)
TRIMMING FOR HIGHER ACCURACY
Calibration error at 25C 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.
+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.
CALIBRATION ERROR, ABSOLUTE ACCURACY AND NONLINEARITY SPECIFICATIONS
TMP17
R 100 950
VOUT = 1mV/K
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 25C, and the error over temperature from 40C to 105C. 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 A/K output. Figure 2 graphically depicts the guaranteed limits of accuracy for a TMP17GS. 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.
Figure 9. Basic Voltage Output (Single Temperature Trim)
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
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
If greater accuracy is desired, initial calibration and scale factor errors can be removed by using the TMP17 in the circuit of Figure 11.
97.6k +5V 8.66k R1 1k R2 5k
OP196
VOUT = 100mV/oC
REF43
7.87k
ment ( JA). Self-heating error in C can be derived by multiplying the power dissipation by JA. Because errors of this type can vary widely for surroundings with different heat sinking capacities, it is necessary to specify 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 25C with a 5 V supply the magnitude of the error is 0.2C or less. A small glued-on heat sink will reduce the temperature error in high temperature, large supply voltage situations.
Table I. Thermal Characteristics
TMP17
V-
Medium Still Air Moving Air @ 500 FPM Fluorinert Liquid
JA ( C/watt) 158 60 35
(sec)* 52 10 2
Figure 11. Two Temperature Trim Circuit
With the transducer at 0C 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.
SUPPLY VOLTAGE AND THERMAL ENVIRONMENT EFFECTS
NOTES * 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.
Response of the TMP17 output to abrupt changes in ambient temperature can be modeled by a single time constant exponential function. Figures 3 and 4 show typical response time plots for media of interest. The time constant, , is dependent on JA and the thermal capacities of the chip and the package. Table I lists the effective (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.
MOUNTING CONSIDERATIONS
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.
2.0
1.0 TOTAL ERROR - C
0
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 40C and 105C. 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.
APPLICATIONS
1.0
2.0
40
25
0
25 TEMPERATURE - C
75
105
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.
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 -5-
TMP17
+5V +15V
TMP17 TMP17 TMP17 TMP17
333.3 (0.1%) VTAVG (1mV/K) 10k (0.1%) VTAVG (10mV/K)
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 A/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. 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 k systems. In this circuit the 1 A/K output of the TMP17 is amplified to 1 mA/C and offset so that 4 mA is equivalent to 17C and 20 mA is equivalent to 33C. 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.
+20V
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.
+V 10k
TMP17
R1 50k 5M
OP196
VOUT = (T1 - T2) x 10k (10mV/oC)
TMP17
REF01E
35.7k
17 C 4mA 33 C 20A 1mA/ C
-V
TMP17
10mV/ C
RT 5k OP97
Figure 14. Differential Measurements
R1 can be used to trim out the inherent offset between the two devices. By increasing the gain resistor (10 k) temperature measurements can be made with higher resolution. If the magnitude of V and V is not the same, the difference in power consumption between the two devices can cause a differential self-heating error. 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 +7.5V J K T E S R APPROX. R VALUE 52 41 41 61 6 6 +5V
C
10k
12.7k
5k
500
10
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.
ROFFSET ROFFSET R RCAL RGAIN C F 9.1k 9.8k RGAIN 100k 180k
REF43
2.5V
OP196
VOUT = 100mV/( C OR F)
2.5V MEASURING JUNCTION Cu
REF43
10k 1k
ROFFSET/RGAIN
OP193
VOUT V-
TMP17
TMP17
Cu R REFERENCE JUNCTION
100k
RG2 (1k) RG1
Figure 17. Temperature to Digital Output
Figure 15. Thermocouple Cold Junction Compensation
By using a differential input A/D converter and choosing the current to voltage conversion resistor correctly, any range of temperatures (up to the 145C 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 1C.
-6-
REV. 0
TMP17
A variable temperature controlling thermostat can easily be built using the TMP17 in the circuit of Figure 18.
+15V
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. 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.
COLUMN SELECT +15V ROW SELECT
10V
REF01E
RPULL-UP RHIGH 62.7k RSET 10k AD790 COMPARATOR
TMP17
TEMP > SETPOINT OUTPUT HIGH TEMP < SETPOINT OUTPUT LOW
4028 BCD TO DECIMAL DECODER
RHYST 10k C RLOW 27.3k C
(OPTIONAL) VOUT AD7501 8-CHANNEL MUX 10k
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 25C to 105C. 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. 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 -15V
+15V -15V
EN 80 - TMP17s
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.
ROFFSET +5V ROFFSET R RCAL RGAIN C F 9.1k 9.8k RGAIN 100k 180k
VOUT T8 T2 T1 REMOTE TMP17s S1 S2 S8
AD7501
D E C O D E R / TTL DTL TO CMOS I/O V- EN CHANNEL SELECT D R I V E R 10k
REF43
2.5V
OP196
VOUT = 100mV/(oC OR oF)
ROFFSET/RGAIN
TMP17
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).
8-Lead Narrow-Body SOIC (SO-8)
C2154-8-7/96
0.0196 (0.50) x 45 0.0099 (0.25) 8 0 0.0500 (1.27) 0.0160 (0.41)
0.1968 (5.00) 0.1890 (4.80)
8 1 5 4
0.1574 (4.00) 0.1497 (3.80)
0.2440 (6.20) 0.2284 (5.80)
PIN 1 0.0098 (0.25) 0.0040 (0.10)
0.0688 (1.75) 0.0532 (1.35)
SEATING PLANE
0.0500 0.0192 (0.49) (1.27) 0.0138 (0.35) BSC
0.0098 (0.25) 0.0075 (0.19)
-8-
REV. 0
PRINTED IN U.S.A.

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