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| a FEATURES Low Voltage Operation (+2.7 V to +5.5 V) Calibrated Directly in C 10 mV/ C Scale Factor (20 mV/ C on TMP37) 2 C Accuracy Over Temperature (typ) 0.5 C Linearity (typ) Stable with Large Capacitive Loads Specified -40 C to +125 C, Operation to +150 C Less than 50 A Quiescent Current Shutdown Current 0.5 A max Low Self-Heating APPLICATIONS Environmental Control Systems Thermal Protection Industrial Process Control Fire Alarms Power System Monitors CPU Thermal Management Low Voltage Temperature Sensors TMP35/TMP36/TMP37 FUNCTIONAL BLOCK DIAGRAM +Vs (2.7V to 5.5V) TMP35 SHUTDOWN TMP36 TMP37 VOUT PACKAGE TYPES AVAILABLE RT-5 (SOT-23) VOUT 1 +VS 2 NC 3 TOP VIEW (Not to Scale) 4 SHUTDOWN 5 GND PRODUCT DESCRIPTION NC = NO CONNECT The TMP35, TMP36 and TMP37 are low voltage, precision centigrade temperature sensors. They provide a voltage output that is linearly proportional to the Celsius (Centigrade) temperature. The TMP35/TMP36/TMP37 do not require any external calibration to provide typical accuracies of 1C at +25C and 2C over the -40C to +125C temperature range. The low output impedance of the TMP35/TMP36/TMP37, and its linear output and precise calibration simplify interfacing to temperature control circuitry and A/D converters. All three devices are intended for single-supply operation from 2.7 V to 5.5 V maximum. Supply current runs well below 50 A providing very low self-heating--less than 0.1C in still air. In addition, a shutdown function is provided to cut supply current to less than 0.5 A. The TMP35 is functionally compatible with the LM35/LM45 and provides a 250 mV output at +25C. The TMP35 reads temperatures from +10C to +125C. The TMP36 is specified from -40C to +125C, provides a 750 mV output at +25C and operates to +125C from a single 2.7 V supply. The TMP36 is functionally compatible with the LM50. Both the TMP35 and TMP36 have an output scale factor of +10 mV/C. The TMP37 is intended for applications over the range +5C to +100C, and provides an output scale factor of 20 mV/C. The TMP37 provides a 500 mV output at +25C. Operation extends to +150C with reduced accuracy for all devices when operating from a 5 V supply. The TMP35/TMP36/TMP37 are all available in low cost 3-pin TO-92, and SO-8 and 5-pin SOT-23 surface mount packages. REV. A 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. SO-8 VOUT 1 NC 2 8 +VS 7 NC TOP VIEW NC 3 (Not to Scale) 6 NC GND 4 5 SHUTDOWN NC = NO CONNECT TO-92 1 2 3 BOTTOM VIEW (Not to Scale) PIN 1 - +Vs, PIN 2 - VOUT, PIN 3 - GND One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 World Wide Web Site: http://www.analog.com Fax: 617/326-8703 (c) Analog Devices, Inc., 1997 TMP35/TMP36/TMP37F/G-SPECIFICATIONS1 unless otherwise noted) Parameter ACCURACY TMP35/TMP36/TMP37F TMP35/TMP36/TMP37G TMP35/TMP36/TMP37F TMP35/TMP36/TMP37G Scale Factor, TMP35 Scale Factor, TMP36 Scale Factor, TMP37 Symbol Conditions TA = +25C TA = +25C Over Rated Temperature Over Rated Temperature +10C TA +125C -40C TA +125C +5C TA +85C +5C TA +100C 3.0 V +VS 5.5 V 0 A IL 50 A TA = +25C 3.0 V +VS 5.5 V TA = +150C for 1 kHrs VIH VIL VS = 2.7 V VS = 5.5 V TA = +25C TA = +25C TA = +25C IL ISC CL 100 0 Note 2 No Oscillations2 Output within 1C 100 k 100 pF Load2 1000 10000 0.5 1.8 Min Typ 1 1 2 2 +10 +10 +20 +20 1 30 50 0.5 0.4 (VS = +2.7 V to +5.5 V, -40 C TA +125 C Max 2 3 3 4 +9.8/+10.2 +9.8/+10.2 +19.6/+20.4 +19.6/+20.4 20 100 Units C C C C mV/C mV/C mV/C mV/C mC/A mC/V mC/V C C V mV mV mV mV mV A A pF ms Load Regulation Power Supply Rejection Ratio Linearity Long-Term Stability SHUTDOWN Logic High Input Voltage Logic Low Input Voltage OUTPUT TMP35 Output Voltage TMP36 Output Voltage TMP37 Output Voltage Output Voltage Range Output Load Current Short-Circuit Current Capacitive Load Driving Device Turn-On Time POWER SUPPLY Supply Range Supply Current Supply Current (Shutdown) NOTES 1 Does not consider errors caused by self-heating. 2 Guaranteed but not tested. Specifications subject to change without notice. PSRR PSRR 400 250 750 500 2000 50 250 1 +VS ISY (ON) ISY (OFF) 2.7 Unloaded Unloaded 0.01 5.5 50 0.5 V A A -2- REV. A TMP35/TMP36/TMP37 WAFER TEST LIMITS (V = +5 V, GND = O V, T = +25 C, unless otherwise noted) S A Parameter ACCURACY Scale Factor Deviation Power Supply Rejection Ratio SHUTDOWN Logic High Input Voltage Logic Low Input Voltage OUTPUT TMP35 Output Voltage TMP36 Output Voltage TMP37 Output Voltage Short-Circuit Current Device Turn-On Time POWER SUPPLY Supply Range Supply Current Supply Current (Shutdown) Symbol Conditions TA = +25C 2.7 V +VS 5.5 V VS = 2.7 V VS = 5.5 V TA = +25C TA = +25C TA = +25C VS = 5.5 V Output within 1C 100 k 100 pF Load1 Min Typ Max 2 Units C mC/V V mV mV mV mV A ms PSRR VIH VIL 30 1.8 400 250 750 500 0.5 250 1 ISC V+ ISY (ON) ISY (OFF) 2.7 Unloaded at +5 V Unloaded at +5 V 5.5 50 0.5 V A A NOTES Electrical tests are performed at wafer probe to the limits shown. Due to variations in assembly methods and normal yield loss, yield after packaging is not guaranteed for standard product dice. Consult factory to negotiate specifications based on dice lot qualification through sample lot assembly and testing. 1 Guaranteed but not tested. DICE CHARACTERISTICS Die Size 0.027 x 0.030 inch, 810 sq. mils (0.685 x 0.762 mm, 0.522 sq. mm) TRANSISTOR COUNT: 25 Substrate is connected to +V S 1. VOUT 1 4 2. GND 3. SHUTDOWN 4. +VS 2 3 For additional DICE ordering information, refer to databook. 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 TMP35/TMP36/TMP37 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 REV. A -3- TMP35/TMP36/TMP37 ABSOLUTE MAXIMUM RATINGS* FUNCTIONAL DESCRIPTION Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +7 V Shutdown Pin . . . . . . . . . . . . . . GND SHUTDOWN +VS Output Pin . . . . . . . . . . . . . . . . . . . . . . GND VOUT +VS Operating Temperature Range . . . . . . . . . . -55C to +150C Dice Junction Temperature . . . . . . . . . . . . . . . . . . . . . +175C Storage Temperature Range . . . . . . . . . . . . -65C to +160C Lead Temperature (Soldering, 60 sec) . . . . . . . . . . . . +300C *CAUTION 1. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation at or above this specification is not implied. Exposure to the above maximum rating conditions for extended periods may affect device reliability. 2. Digital inputs are protected; however, permanent damage may occur on unprotected units from high-energy electrostatic fields. Keep units in conductive foam or packaging at all times until ready to use. Use proper antistatic handling procedures. 3. Remove power before inserting or removing units from their sockets. Package Type TO-92 (T9 Suffix) SO-8 (S Suffix) SOT-23 (RT Suffix) JA JC An equivalent circuit for the TMP3x family of micropower, centigrade temperature sensors is shown in Figure 1. At the heart of the temperature sensor is a bandgap core, which is comprised of transistors Q1 and Q2, biased by Q3 to approximately 8 A. The bandgap core operates both Q1 and Q2 at the same collector current level; however, since the emitter area of Q1 is 10 times that of Q2, Q1's VBE and Q2's VBE are not equal by the following relationship: A VBE =VT x ln E ,Q1 AE ,Q2 +VS SHDN 25A 3X 2X Units C/W C/W C/W +VOUT 7.5A Q3 6X 2X Q4 Q1 10X R3 R2 Q2 1X R1 162 158 300 120 43 180 JA is specified for device in socket (worst case conditions). ORDERING GUIDE Model TMP35FT9 TMP35GT9 TMP35FS TMP35GS TMP35GRT2 TMP36FT9 TMP36GT9 TMP36FS TMP36GS TMP36GRT2 TMP37FT9 TMP37GT9 TMP37FS TMP37GS TMP37GRT2 Accuracy at 25 C ( C max) 2.0 3.0 2.0 3.0 3.0 2.0 3.0 2.0 3.0 3.0 2.0 3.0 2.0 3.0 3.0 Linear Operating Temperature Range +10C to +125C +10C to +125C +10C to +125C +10C to +125C +10C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C +5C to +100C +5C to +100C +5C to +100C +5C to +100C +5C to +100C Package Options1 TO-92 TO-92 SO-8 SO-8 RT-5 TO-92 TO-92 SO-8 SO-8 RT-5 TO-92 TO-92 SO-8 SO-8 RT-5 GND Figure 1. Temperature Sensor Simplified Equivalent Circuit Resistors R1 and R2 are used to scale this result to produce the output voltage transfer characteristic of each temperature sensor and, simultaneously, R2 and R3 are used to scale Q1's VBE as an offset term in VOUT. Table I summarizes the differences between the three temperature sensors' output characteristics: Table I. TMP3x Output Characteristics Sensor TMP35 TMP36 TMP37 Offset Voltage (V) 0 0.5 0 Output Voltage Scaling (mV/ C) 10 10 20 Output Voltage @ 25 C 250 mV 750 mV 500 mV NOTES 1 SO = Small Outline; RT = Plastic Surface Mount; TO = Plastic. 2 Consult factory for availability. The output voltage of the temperature sensor is available at the emitter of Q4, which buffers the bandgap core and provides load current drive. Q4's current gain, working with the available base current drive from the previous stage, sets the short-circuit current limit of these devices to 250 A. -4- REV. A TMP35/TMP36/TMP37 2.0 a. TMP35 1.8 1.6 OUTPUT VOLTAGE - Volts 100 b. TMP36 c. TMP37 VS = 3V b c 31.6 10 3.16 1 0.32 0.1 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 50 a POWER SUPPLY REJECTION - C/V 0.032 0.01 20 25 0 25 50 75 TEMPERATURE - C 100 125 100 1k FREQUENCY - Hz 10k 100k Figure 2. Output Voltage vs. Temperature Figure 5. Power Supply Rejection vs. Frequency 5 4 3 ACCURACY ERROR - C MINIMUM SUPPLY VOLTAGE - Volts 5 4 MINIMUM SUPPLY VOLTAGE REQUIRED TO MEET DATA SHEET SPECIFICATION NO LOAD 2 1 0 1 a a. MAXIMUM LIMIT ( G GRADE ) b. TYPICAL ACCURACY ERROR c. MINIMUM LIMIT ( G GRADE ) 3 b 2 a b 2 3 4 5 0 20 40 60 80 100 TEMPERATURE - C 120 140 c 1 a. TMP35/TMP36 b. TMP37 0 50 25 0 25 50 75 TEMPERATURE - C 100 125 Figure 3. Accuracy Error vs. Temperature Figure 6. Minimum Supply Voltage vs. Temperature 0.4 V+ = +3V to +5.5V, NO LOAD POWER SUPPLY REJECTION - C/V 60 a. V+ = 5V b. V+ = 3V 50 SUPPLY CURRENT - A 0.3 NO LOAD 40 a 30 0.2 0.1 20 b 0 50 25 0 25 50 75 TEMPERATURE - C 100 125 10 50 25 0 25 50 75 TEMPERATURE - C 100 125 Figure 4. Power Supply Rejection vs. Temperature Figure 7. Supply Current vs. Temperature REV. A -5- TMP35/TMP36/TMP37 50 TA = +25C, NO LOAD 40 SUPPLY CURRENT - A 400 = SHUTDOWN PIN HIGH TO LOW (3V TO 0V) 300 RESPONSE TIME - s 30 200 20 100 10 = SHUTDOWN PIN LOW TO HIGH (0V TO 3V) VOUT SETTLES WITHIN 1C 0 0 1 2 3 4 5 6 SUPPLY VOLTAGE - Volts 7 8 0 50 25 0 25 50 75 TEMPERATURE - C 100 125 Figure 8. Supply Current vs. Supply Voltage Figure 11. VOUT Response Time for Shutdown Pin vs. Temperature 50 a. V+ = 5V b. V+ = 3V OUTPUT VOLTAGE - Volts 1.0 0.8 0.6 0.4 0.2 0 1.0 0.8 0.6 0.4 b 40 SUPPLY CURRENT - nA NO LOAD 30 TA = 25C V+ = 3V SHUTDOWN = SIGNAL 20 a 10 TA = 25C V+ AND SHUTDOWN = SIGNAL 0.2 125 0 50 25 0 25 50 75 TEMPERATURE - C 100 0 50 0 50 100 150 200 250 TIME - s 300 350 400 450 Figure 9. Supply Current vs. Temperature (Shutdown = 0 V) Figure 12. VOUT Response Time to Shutdown and V+ Pins vs. Time 110 100 90 PERCENT OF CHANGE - % 400 a 300 RESPONSE TIME - s = V+ AND SHUTDOWN PINS HIGH TO LOW (3V TO 0V) 80 70 60 50 40 b c VIN = +3V, +5V 200 = V+ AND SHUTDOWN PINS LOW TO HIGH (0V TO 3V) VOUT SETTLES WITHIN 1C 100 a. TMP35 SOIC SOLDERED TO .5" x .3" Cu PCB 30 20 10 b. TMP36 SOIC SOLDERED TO .6" x .4" Cu PCB c. TMP35 TO-92 IN SOCKET SOLDERED TO 1" x .4" Cu PCB 0 50 25 0 25 50 75 TEMPERATURE - C 100 125 0 0 100 200 300 TIME - sec 400 500 600 Figure 10. VOUT Response Time for V+ Power-Up/PowerDown vs. Temperature Figure 13. Thermal Response Time in Still Air -6- REV. A TMP35/TMP36/TMP37 140 120 100 a. TMP35 SOIC SOLDERED TO .5" x .3" Cu PCB b. TMP36 SOIC SOLDERED TO .6" x .4" Cu PCB TIME CONSTANT - sec 100 90 10mV 1ms c. TMP35 TO-92 IN SOCKET SOLDERED TO 1" x .4" Cu PCB VOLT/DIVISION 80 VIN = +3V, +5V 60 b 40 c 20 0 0 100 200 a 300 400 500 AIR VELOCITY - FPM 600 700 10 0% TIME/DIVISION Figure 14. Thermal Response Time Constant in Forced Air Figure 16. Temperature Sensor Wideband Output Noise Voltage. Gain = 100, BW = 157 kHz 110 100 90 80 CHANGE - % a 2400 2200 VOLTAGE NOISE DENSITY - nV/ Hz 2000 1800 1600 1400 1200 1000 800 600 c b VIN = +3V, +5V b 70 60 50 40 a. TMP35 SOIC SOLDERED TO .5" x .3" Cu PCB 30 20 10 0 0 10 20 30 TIME - sec 40 50 60 b. TMP36 SOIC SOLDERED TO .6" x .4" Cu PCB c. TMP35 TO-92 IN SOCKET SOLDERED TO 1" x .4" Cu PCB a 400 200 0 10 a. TMP35/36 b. TMP37 100 1k FREQUENCY - Hz 10k Figure 15. Thermal Response Time in Stirred Oil Bath Figure 17. Voltage Noise Spectral Density vs. Frequency APPLICATIONS SECTION Shutdown Operation Mounting Considerations All TMP3x devices include a shutdown capability that reduces the power supply drain to less than 0.5 A, maximum. This feature, available only in the SO-8 and the SOT-23 packages, is TTL/CMOS level compatible, provided that the temperature sensor supply voltage is equal in magnitude to the logic supply voltage. Internal to the TMP3x at the SHUTDOWN pin, a pull-up current source to VIN is connected. This permits the SHUTDOWN pin to be driven from an open-collector/drain driver. A logic LOW, or zero-volt condition on the SHUTDOWN pin, is required to turn the output stage OFF. During shutdown, the output of the temperature sensors becomes a high impedance state where the potential of the output pin would then be determined by external circuitry. If the shutdown feature is not used, it is recommended that the SHUTDOWN pin be connected to VIN (Pin 8 on the SO-8, Pin 2 on the SOT-23). The shutdown response time of these temperature sensors is illustrated in Figures 10, 11 and 12. If the TMP3x temperature sensors are thermally attached and protected, they can be used in any temperature measurement application where the maximum temperature range of the medium is between -40C to +125C. Properly cemented or glued to the surface of the medium, these sensors will be within 0.01C of the surface temperature. Caution should be exercised, especially with TO-92 packages, because the leads and any wiring to the device can act as heat pipes, introducing errors if the surrounding air-surface interface is not isothermal. Avoiding this condition is easily achieved by dabbing the leads of the temperature sensor and the hookup wires with a bead of thermally conductive epoxy. This will ensure that the TMP3x die temperature is not affected by the surrounding air temperature. Because plastic IC packaging technology is used, excessive mechanical stress should be avoided when fastening the device with a clamp or a screw-on heat tab. Thermally conductive epoxy or glue, which must be electrically nonconductive, is recommended under typical mounting conditions. REV. A -7- TMP35/TMP36/TMP37 These temperature sensors, as well as any associated circuitry, should be kept insulated and dry to avoid leakage and corrosion. In wet or corrosive environments, any electrically isolated metal or ceramic well can be used to shield the temperature sensors. Condensation at very cold temperatures can cause errors and should be avoided by sealing the device, using electrically nonconductive epoxy paints or dip or any one of many printed circuit board coatings and varnishes. Thermal Environment Effects Basic Temperature Sensor Connections The thermal environment in which the TMP3x sensors are used determines two important characteristics: self-heating effects and thermal response time. Illustrated in Figure 18 is a thermal model of the TMP3x temperature sensors that is useful in understanding these characteristics. TJ JC TC CA The circuit in Figure 19 illustrates the basic circuit configuration for the TMP3x family of temperature sensors. The table shown in the figure illustrates the pin assignments of the temperature sensors for the three package types. For the SOT-23, Pin 3 is labeled as "NC" are as Pins 2, 3, 6 and 7 on the SO-8 package. It is recommended that no electrical connections be made to these pins. If the shutdown feature is not needed on the SOT-23 or the SO-8 package, the SHUTDOWN pin should be connected to VS. 2.7V < Vs < 5.5V 0.1F Vs SHDN TMP3x GND VOUT PD CCH CC TA PIN ASSIGNMENTS PACKAGE VS 8 2 1 GND 4 5 3 VOUT 1 1 2 SHDN 5 4 NA Figure 18. TMP3x Thermal Circuit Model In the TO-92 package, the thermal resistance junction-to-case, JC, is 120C/W. The thermal resistance case-to-ambient, CA, is the difference between JA and JC, and is determined by the characteristics of the thermal connection. The temperature sensor's power dissipation, represented by PD, is the product of the total voltage across the device and its total supply current (including any current delivered to the load). The rise in die temperature above the medium's ambient temperature is given by: SO-8 SOT-23-5 TO-92 Figure 19. Basic Temperature Sensor Circuit Configuration TJ = P D x J C + CA +T A Thus, the die temperature rise of a TMP35 "RT" package mounted into a socket in still air at 25C and driven from a +5 V supply is less than 0.04C. The transient response of the TMP3x sensors to a step change in the temperature is determined by the thermal resistances and the thermal capacities of the die, CCH, and the case, CC. The thermal capacity of the case, CC, varies with the measurement medium since it includes anything in direct contact with the package. In all practical cases, the thermal capacity of the case is the limiting factor in the thermal response time of the sensor and can be represented by a single-pole RC time constant response. Figures 13 and 15 illustrate the thermal response time of the TMP3x sensors under various conditions. The thermal time constant of a temperature sensor is defined as the time required for the sensor to reach 63.2% of the final value for a step change in the temperature. For example, the thermal time constant of a TMP35 "S" package sensor mounted onto a 0.5" by 0.3" PCB is less than 50 sec in air, whereas in a stirred oil bath the time constant is less than 3 sec. ( ) Note the 0.1 F bypass capacitor on the input. This capacitor should be a ceramic type, have very short leads (surface mount would be preferable), and located as close a physical proximity to the temperature sensor supply pin as practical. Since these temperature sensors operate on very little supply current and could be exposed to very hostile electrical environments, it is important to minimize the effects of RFI (Radio-Frequency Interference) on these devices. The effect of RFI on these temperature sensors in specific and analog ICs in general is manifested as abnormal dc shifts in the output voltage due to the rectification of the high frequency ambient noise by the IC. In those cases where the devices are operated in the presence of high frequency radiated or conducted noise, a large value tantalum capacitor ( 2.2 F) placed across the 0.1 F ceramic may offer additional noise immunity. Fahrenheit Thermometers Although the TMP3x temperature sensors are centigrade temperature sensors, a few components can be used to convert the output voltage and transfer characteristics to directly read Fahrenheit temperatures. Shown in Figure 20a is an example of a simple Fahrenheit thermometer using either the TMP35 or the TMP37. This circuit can be used to sense temperatures from 41F to 257F, with an output transfer characteristic of 1 mV/F using the TMP35, and from 41F to 212F using the TMP37 with an output characteristic of 2 mV/F. This particular approach does not lend itself well to the TMP36 because of its inherent 0.5 V output offset. The circuit is constructed with an AD589, a 1.23 V voltage reference, and four resistors whose values for each sensor are shown in the figure table. The scaling of the -8- REV. A TMP35/TMP36/TMP37 output resistance levels was to ensure minimum output loading on the temperature sensors. A generalized expression for the circuit's transfer equation is given by: VS VS 0.1F R1 R3 VOUT = TMP 35 + R3 + R4 AD589 R1+ R2 ( ) ( ) TMP36 GND VOUT R1 45.3k where: TMP35 = Output voltage of the TMP35, or the TMP37, at the measurement temperature, TM, and AD589 = Output voltage of the reference = 1.23 V. Note that the output voltage of this circuit is not referenced to the circuit's common. If this output voltage were to be applied directly to the input of an ADC, the ADC's common should be adjusted accordingly. R2 10k VOUT @ 1mV/ F - 58 F VOUT @ -40 F = 18mV VS 0.1 F VS R1 VOUT @ 257 F = 315mV Figure 20b. TMP36 Fahrenheit Thermometer Version 1 TMP35/37 GND VOUT R2 VOUT AD589 1.23V R3 R4 At the expense of additional circuitry, the offset produced by the circuit in Figure 20b can be avoided by using the circuit in Figure 20c. In this circuit, the output of the TMP36 is conditioned by a single-supply, micropower op amp, the OP193. Although the entire circuit operates from a single +3 V supply, the output voltage of the circuit reads the temperature directly, with a transfer characteristic of 1 mV/F, without offset. This is accomplished through the use of an ADM660, a supply voltage inverter. The +3 V supply is inverted and applied to the P193's V- terminal. Thus, for a temperature range between -40F and 257F, the output of the circuit reads -40 mV to 257 mV. A general expression for the circuit's transfer equation is given by: PIN ASSIGNMENTS SENSOR TMP35 TMP37 TCVOUT R1 (k ) R2 (k ) R3 (k ) R4 (k ) 1mV/ F 2mV/ F 45.3 45.3 10 10 10 10 374 182 R6 R4 R4 VS VOUT = 1+ R3 TMP 36 - R3 2 R5 + R6 ( ) Average and Differential Temperature Measurement Figure 20a. TMP35/TMP37 Fahrenheit Thermometers The same circuit principles can be applied to the TMP36, but because of the TMP36's inherent offset, the circuit uses two less resistors as shown in Figure 20b. In this circuit, the output voltage transfer characteristic is 1 mV/F, but is referenced to the circuit's common; however, there is a 58 mV (58F) offset in the output voltage. For example, the output voltage of the circuit would read 18 mV, were the TMP36 placed in -40F ambient environment, and 315 mV at 257F. In many commercial and industrial environments, temperature sensors are often used to measure the average temperature in a building, or the difference in temperature between two locations on a factory floor or in an industrial process. The circuits in Figures 21a and 21b demonstrate an inexpensive approach to average and differential temperature measurement. In Figure 21a, an OP193 is used to sum the outputs of three temperature sensors to produce an output voltage scaled by 10 mV/C that represents the average temperature at three locations. The circuit can be extended to as many temperature sensors as required as long as the circuit's transfer equation is maintained. In this application, it is recommended that one temperature sensor type be used throughout the circuit; otherwise, the output voltage of the circuit will not produce an accurate reading of the various ambient conditions. REV. A -9- TMP35/TMP36/TMP37 +3V R1 50k R2 50k VS VOUT R5 R6 GND 1 NC ELEMENT R2 R4 R5 R6 TMP36 258.6k 10k 47.7k 10k 10 F 2 8 5 -3V 10 F C1 10 F 8 2 VOUT @ 1mV/ F 6 -40 F TA 257 F R3 R4 0.1 F 10 F/0.1 F TMP36 3 OP193 4 ADM660 4 3 6 NC 7 Figure 20c. TMP36 Fahrenheit Thermometer Version 2 2.7V < +VS < 5.5V 0.1 F 7 1 3 VTEMP(AVG) @ 10mV/ C FOR TMP35/36 @ 20mV/ C FOR TMP35/36 2 as shown in the figure. Using the TMP36, the output voltage of the circuit is scaled by 10 mV/C. To minimize error in the difference between the two measured temperatures, a common, readily available thin-film resistor network is used for R1-R4. 2.7V < VS < 5.5V OP193 4 R5 100k R1 300k TMP3x 0.1 F R2 300k R6 7.5k TMP36 @T1 R1* R8 25k R2* TMP3x FOR R1 = R2 = R3 = R; R3 300k VTEMP(AVG) = 1 (TMP3x1 + TMP3x2+ TMP3x3) 3 R5 = R1 3 R4 = R6 0.1 F 7 2 R3* R9 25k 6 VOUT TMP3x R4 7.5k OP193 3 4 0.1 F TMP36 @T2 R7 100k Figure 21a. Configuring Multiple Sensors for Average Temperature Measurements CENTERED AT R4* 1F The circuit in Figure 21b illustrates how a pair of TMP3x sensors can be used with an OP193 configured as a difference amplifier to read the difference in temperature between two locations. In these applications, it is always possible that one temperature sensor would be reading a temperature below that of the other sensor. To accommodate this condition, the output of the OP193 is offset to a voltage at one-half the supply via R5 and R6. Thus, the output voltage of the circuit is measured relative to this point, 0 TA 125C R5 100k R6 100k VOUT = T2 - T1 @ 10mV/ C V CENTERED AT S 2 *R1-R4, CADDOCK T914-100k-100, OR EQUIVALENT Figure 21b. Configuring Multiple Sensors for Differential Temperature Measurements -10- REV. A TMP35/TMP36/TMP37 Microprocessor Interrupt Generator These inexpensive temperature sensors can be used with a voltage reference and an analog comparator to configure an interrupt generator useful in microprocessor applications. With the popularity of fast 486 and Pentium* laptop computers, the need to indicate a microprocessor over-temperature condition has grown tremendously. The circuit illustrated in Figure 22 demonstrates one way to generate an interrupt using a TMP35, a CMP402 analog comparator, and a REF191, a 2 V precision voltage reference. The circuit has been designed to produce a logic HIGH interrupt signal if the microprocessor temperature exceeds 80C. This 80C trip point was arbitrarily chosen (final value set by the microprocessor thermal reference design) and is set using an R3-R4 voltage divider of the REF191's output voltage. Since the output of the TMP35 is scaled by 10 mV/C, the voltage at the CMP402's inverting terminal is set to 0.8 V. Since temperature is a slowly moving quantity, the possibility for comparator chatter exists. To avoid this condition, hysteresis is used around the comparator. In this application, a hysteresis of 5C about the trip point was arbitrarily chosen; the ultimate value for hysteresis should be determined by the end application. The output logic voltage swing of the comparator with R1 and R2 determine the amount of comparator hysteresis. Using a 3.3 V supply, the output logic voltage swing of the CMP402 is 2.6 V; thus, for a hysteresis of 5C (50 mV @ 10 mV/C), R1 is set to 20 k and R2 is set to 1 M. An expression for this circuit's hysteresis is given by: R1 VHYS = VLOGIC SWING, CMP402 R2 Thermocouple Signal Conditioning with Cold-Junction Compensation The circuit in Figure 23 conditions the output of a Type K thermocouple, while providing cold-junction compensation, for temperatures between 0C and 250C. The circuit operates from single +3.3 V to +5.5 V supplies and has been designed to produce an output voltage transfer characteristic of 10 mV/C. A Type K thermocouple exhibits a Seebeck coefficient of approximately 41 V/C; therefore, at the cold junction, the TMP35, with a temperature coefficient of 10 mV/C, is used with R1 and R2 to introduce an opposing cold-junction temperature coefficient of -41 V/C. This prevents the isothermal, cold-junction connection between the circuit's PCB tracks and the thermocouple's wires from introducing an error in the measured temperature. This compensation works extremely well for circuit ambient temperatures in the range of 20C to 50C. Over a 250C measurement temperature range, the thermocouple produces an output voltage change of 10.151 mV. Since the required circuit's output full-scale voltage is 2.5 V, the gain of the circuit is set to 246.3. Choosing R4 equal to 4.99 k sets R5 equal to 1.22 M. Since the closest 1% value for R5 is 1.21 M, a 50 k potentiometer is used with R5 for fine trim of the full-scale output voltage. Although the OP193 is a superior single-supply, micropower operational amplifier, its output stage is not rail-to-rail; as such, the 0C output voltage level is 0.1 V. If this circuit were to be digitized by a single-supply ADC, the ADC's common should be adjusted to 0.1 V accordingly. Using TMP3x Sensors in Remote Locations ( ) Since the likelihood that this circuit would be used in close proximity to high speed digital circuits, R1 is split into equal values and a 1000 pF is used to form a low-pass filter on the output of the TMP35. Furthermore, to prevent high frequency noise from contaminating the comparator trip point, a 0.1 F capacitor is used across R4. *All trademarks are the property of their respective holders. 3.3V In many industrial environments, sensors are required to operate in the presence of high ambient noise. These noise sources take on many forms; for example, SCR transients, relays, radio transmitters, arc welders, ac motors, et cetera. They may also be used at considerable distance from the signal conditioning circuitry. These high noise environments are very typically in the form of electric fields, so the voltage output of the temperature sensor can be susceptible to contamination from these noise sources. R2 1M VS VOUT 0.1 F R1A 10k CL 1000pF 0.1 F 2 R3 16k R4 10k VREF 13 R1B 10k 3 6 5 4 0.1 F TMP35 R5 100k GND C1 2 14 INTERRUPT >80 C <80 C 3 REF191 4 6 1F 0.1 F C1 = 1 CMP402 4 Figure 22. Pentium Over-Temperature Interrupt Generator REV. A -11- TMP35/TMP36/TMP37 3.3V < VS < 5.5V VS 0.1 F VOUT R3 10M 5% R4 4.99k R5* 1.21M 0.1 F R1* 24.9k 2 6 CHROMEL TYPE K THERMO COUPLE ALUMEL CU 7 P1 50k TMP35 GND OP193 3 4 R6 100k 5% VOUT 0 - 2.5V COLD JUNCTION CU R2* 102 NOTE: ALL RESISTORS 1% UNLESS OTHERWISE NOTED 0C T 250 C ISOTHERMAL BLOCK Figure 23. A Single-Supply, Type K Thermocouple Signal Conditioning Circuit with Cold-Junction Compensation Illustrated in Figure 24 is a way to convert the output voltage of a TMP3x sensor into a current to be transmitted down a long twisted-pair shielded cable to a ground referenced receiver. The temperature sensors do not possess the capability of high output current operation; thus, a garden variety PNP transistor is used to boost the output current drive of the circuit. As shown in the table, the values of R2 and R3 were chosen to produce an arbitrary full-scale output current of 2 mA. Lower values for the full-scale current are not recommended. The minimum-scale output current produced by the circuit could be contaminated by nearby ambient magnetic fields operating in vicinity of the circuit/cable pair. Because of the use of an external transistor, the minimum recommended operating voltage for this circuit is +5 V. Note, to minimize the effects of EMI (or RFI) both the circuit's and the temperature sensor's supply pins are bypassed with good quality, ceramic capacitors. A Temperature to 4-20 mA Loop Transmitter In many process control applications, two-wire transmitters are used to convey analog signals through noisy ambient environments. These current transmitters use a "zero-scale" signal current of 4 mA that can be used to power the transmitter's signal conditioning circuitry. The "full-scale" output signal in these transmitters is 20 mA. A circuit that transmits temperature information in this fashion is illustrated in Figure 25. Using a TMP3x as the temperature sensor, the output current is linearly proportional to the temperature of the medium. The entire circuit operates from the +3 V output of the REF193. The REF193 requires no external trimming for two reasons: (1) the REF193's tight initial output voltage tolerance and (2) the low supply current of TMP3x, the OP193 and the REF193. The entire circuit consumes less than 3 mA from a total budget of 4 mA. The OP193 regulates the output current to satisfy the current summation at the noninverting node of the OP193. A generalized expression for the KCL equation at the OP193's Pin 3 is given by: R1 4.7k 2N2907 0.1 F 0.01 F VS +5V VOUT 1 TMP 3x x R3 VREF x R3 IOUT = x + R1 R2 R7 For each of the three temperature sensors, the table below illustrates the values for each of the components, P1, P2 and R1-R4: Table II. Circuit Element Values for Loop Transmitter R3 TMP3x GND VOUT R2 TWISTED PAIR BELDEN TYPE 9502 OR EQUIVALENT Sensor TMP35 TMP36 TMP37 R1( ) 97.6 k 97.6 k 97.6 k P1( ) R2( ) 5k 5k 5k 1.58 M 931 k 10.5 k P2( ) R3( ) R4( ) 100 k 50 k 500 140 k 97.6 k 84.5 k 56.2 k 47 k 8.45 k SENSOR TMP35 TMP36 TMP37 R2 634 887 1k R3 634 887 1k Figure 24. A Remote, Two-Wire Boosted Output Current Temperature Sensor -12- REV. A TMP35/TMP36/TMP37 The 4 mA offset trim is provided by P2, and P1 provides the circuit's full-scale gain trim at 20 mA. These two trims do not interact because the noninverting input of the OP193 is held at a virtual ground. The zero-scale and full-scale output currents of the circuit are adjusted according to the operating temperature range of each temperature sensor. The Schottky diode, D1, is required in this circuit to prevent loop supply power-on transients from pulling the noninverting input of the OP193 more than 300 mV below its inverting input. Without this diode, such transients could cause phase reversal of the operational amplifier and possible latchup of the transmitter. The loop supply voltage compliance of the circuit is limited by the maximum applied input voltage to the REF193 and is from +9 V to +18 V. A Temperature to Frequency Converter +5V 0.1 F VS 8 10 F/0.1 F 6 7 1 CT* RPU 5k VOUT 4 3 GND R1 RT* +5V P2 100k P1 5 2 AD654 TMP3x fOUT NB: ATTA (min), fOUT = 0Hz fOUT ROFF1 470 OFFSET ROFF2 10 *RT & CT - SEE TABLE Another common method of transmitting analog information from a remote location is to convert a voltage to an equivalent in the frequency domain. This is readily done with any of the low cost, monolithic voltage-to-frequency converters (VFCs) available. These VFCs feature a robust, open-collector output transistor for easy interfacing to digital circuitry. The digital signal produced by the VFC is less susceptible to contamination from external noise sources and line voltage drops because the only important information is the frequency of the digital signal. As long as the conversions between temperature and frequency are done accurately, the temperature data from the sensors can be reliably transmitted. The circuit in Figure 26 illustrates a method by which the outputs of these temperature sensors can be converted to a frequency using the AD654. The output signal of the AD654 is a square wave that is proportional to the dc input voltage across Pins 4 and 3. The transfer equation of the circuit is given by: SENSOR TMP35 TMP36 TMP37 RT (R1 + P1) 11.8k + 500 16.2k + 500 18.2k + 1k CT 1.7nF 1.8nF 2.1nF Figure 26. A Temperature to Frequency Converter V - VOFFSET f OUT = TMP 10 x RT x CT ( ) An offset trim network (fOUT OFFSET ) is included with this circuit to set fOUT at 0 Hz when the temperature sensor's minimum output voltage is reached. Potentiometer P1 is required to calibrate the absolute accuracy of the AD654. The table in the figure illustrates the circuit element values for each of the three sensors. The nominal offset voltage required for 0 Hz output from the TMP35 is 50 mV; for the TMP36 and TMP37, the offset voltage required is 100 mV. In all cases for the circuit values shown, the output frequency transfer characteristic of the circuit was set at 50 Hz/C. At the receiving end, a frequencyto-voltage converter (FVC) can be used to convert the frequency back to a dc voltage for further processing. One such FVC is the AD650. For complete information on the AD650 and AD654, please consult the individual data sheets for those devices. +3V 6 2 REF193 R2* 1F 4 VLOOP +9V TO +18V VS R1* P2* 4mA ADJUST 3 P1* 20mA ADJUST D1 R3* R4* 2 4 7 0.1 F R6 100k TMP3x VOUT GND Q1 2N1711 VOUT R5 100k RL 250 * SEE TEXT FOR VALUES R7 100 D1 : HP5082-2810 A1 : OP193 IL Figure 25. A Temperature to 4-to-20 mA Loop Transmitter REV. A -13- TMP35/TMP36/TMP37 Driving Long Cables or Heavy Capacitive Loads Although the TMP3x family of temperature sensors is capable of driving capacitive loads up to 10,000 pF without oscillation, output voltage transient response times can be improved with the use of a small resistor in series with the output of the temperature sensor, as shown in Figure 27. As an added benefit, this resistor forms a low-pass filter with the cable's capacitance, which helps to reduce bandwidth noise. Since the temperature sensor is likely to be used in environments where the ambient noise level can be very high, this resistor helps to prevent rectification by the devices of the high frequency noise. The combination of this resistor and the supply bypass capacitor offers the best protection. +VS relates the change in rates of reaction to a change in elevated temperatures, is the Arrhenius model. From the Arrhenius model, an acceleration factor can be calculated and applied to the parameter specified. For example, this acceleration factor can be used to reduce a temperature sensor's long-term stability (e.g., 0.4C after 1000 hours at TJ = 150C) to an observed shift in that parameter at 25C. For any semiconductor device, the acceleration factor is expressed as: E 1 1 F = exp a x - k T1 T 2 where F = Ea = k= T1 = and T2 = Calculated acceleration factor; Activation energy in eV = 0.7 eV; Boltzmann's constant = 8.63 x 10-5 eV/K; Test temperature in Kelvin, TJ = 150C = 423.15 K; Desired operating temperature in Kelvin, TJ = 25C = 298.15 K 0.1 F TMP3x VOUT 750 LONG CABLE OR HEAVY CAPACITIVE LOADS For example, if the desired operating temperature of an IC is 25C and has been subjected to test temperature of 150C, the acceleration factor is: F = 3.23 x 10 -4 GND Figure 27. Driving Long Cables or Heavy Capacitive Loads Commentary on Long-Term Stability The concept of long-term stability has been used for many years to describe by what amount an IC's parameter would shift during its lifetime. This is a concept that has been typically applied to both voltage references and monolithic temperature sensors. Unfortunately, integrated circuits cannot be evaluated at room temperature (25C) for 10 years or so to determine this shift. As a result, manufacturers very typically perform accelerated lifetime testing of integrated circuits by operating ICs at elevated temperatures (between 125C and 150C) over a shorter period of time (typically, between 500 and 1000 hours). As a result of this operation, the lifetime of an integrated circuit is significantly accelerated due to the increase in rates of reaction within the semiconductor material. A well-understood, and universal, model used by the semiconductor industry, that With this background information, the TMP3x family's longterm stability can be mapped to what its equivalent observed shift would be at TA = 25C. As quoted in the data sheet, the long-term stability of these temperature sensors after 1000 hours at 150C is 0.4C. This shift is equivalent to 0.01C/day at TJ = 150C. To determine what the observed shift would be at TA = 25C is a matter of applying the acceleration factor calculated above to this result: 0.01C / day x 3.23 x10 -4 = 0.003mC / day @ 25C Thus, if any of the TMP3x devices were to be used at 25C, the observed shift would be no more than 0.003 mC per day, or 0.1 mC per month. Calculating the observed shift for any other operating temperature is simply a matter of calculating a new acceleration factor. -14- REV. A TMP35/TMP36/TMP37 OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 3-Lead Plastic Package (TO-92) 0.135 (3.43) MIN 0.205 (5.20) 0.175 (4.96) 0.210 (5.33) 0.170 (4.38) SEATING PLANE 0.050 (1.27) MAX 8-Lead SOIC (SO-8) 0.1968 (5.00) 0.1890 (4.80) 8 5 4 0.1574 (4.00) 0.1497 (3.80) 1 0.2440 (6.20) 0.2284 (5.80) 0.500 (12.70) MIN 0.019 (0.482) 0.016 (0.407) SQUARE PIN 1 0.0098 (0.25) 0.0040 (0.10) 0.0688 (1.75) 0.0532 (1.35) 0.0196 (0.50) x 45 0.0099 (0.25) 0.0500 0.0192 (0.49) SEATING (1.27) 0.0098 (0.25) PLANE BSC 0.0138 (0.35) 0.0075 (0.19) 8 0 0.0500 (1.27) 0.0160 (0.41) 0.105 (2.66) 0.095 (2.42) 0.105 (2.66) 0.080 (2.42) 0.055 (1.39) 0.045 (1.15) 5-Lead Surface Mount RT-5 (SOT-23 Type) 0.1181 (3.00) 0.1102 (2.80) 0.105 (2.66) 1 0.080 (2.42) 2 3 0.165 (4.19) 0.125 (3.94) BOTTOM VIEW 0.0669 (1.70) 0.0590 (1.50) PIN 1 5 1 2 4 3 0.1181 (3.00) 0.1024 (2.60) 0.0374 (0.95) BSC 0.0748 (1.90) BSC 0.0512 (1.30) 0.0354 (0.90) 0.0059 (0.15) 0.0019 (0.05) 0.0197 (0.50) 0.0138 (0.35) 0.0571 (1.45) 0.0374 (0.95) SEATING PLANE 10 0 0.0079 (0.20) 0.0031 (0.08) 0.0217 (0.55) 0.0138 (0.35) REV. A -15- -16- C2116a-6-6/97 PRINTED IN U.S.A. |
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