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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) SHUTDOWN TMP35/ 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 NC = NO CONNECT PRODUCT DESCRIPTION RN-8 (SOIC) VOUT 1 NC 2 8 +VS 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-lead TO-92, SOIC-8, and 5-lead SOT-23 surface-mount packages. REV. C 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 that may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. 7 NC TOP VIEW (Not to Scale) 6 NC NC 3 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: 781/329-4700 www.analog.com Fax: 781/326-8703 (c) Analog Devices, Inc., 2002 TMP35/TMP36/TMP37-SPECIFICATIONS1 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 -40C TA +105C -105C TA +125C 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 1.8 Min (VS = 2.7 V to 5.5 V, -40 C TA +125 C, unless Typ 1 1 2 2 10 10 20 20 Max 2 3 3 4 9.8/10.2 9.8/10.2 19.6/20.4 19.6/20.4 Unit C C C C mV/C mV/C mV/C mV/C 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 6 25 30 50 0.5 0.4 20 60 100 mC/A mC/A mC/V mC/V C C V mV mV mV mV mV A A pF ms 400 250 750 500 2000 50 250 10000 0.5 1 +VS ISY (ON) ISY (OFF) 2.7 Unloaded Unloaded 0.01 5.5 50 0.5 V A A 50 40 LOAD REG - m C/ A 30 20 10 0 -50 0 50 TEMPERATURE - C 100 150 Figure 1. Load Reg vs. Temperature (mC/A) -2- REV. C TMP35/TMP36/TMP37 ABSOLUTE MAXIMUM RATINGS 1, 2, 3 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 NOTES 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 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. An equivalent circuit for the TMP3x family of micropower, centigrade temperature sensors is shown in Figure 2. At the heart of the temperature sensor is a band gap core, which is comprised of transistors Q1 and Q2, biased by Q3 to approximately 8 A. The band gap 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 25 A Package Type TO-92 (T9 Suffix) SOIC-8 (S Suffix) SOT-23 (RT Suffix) JA JC Unit C/W C/W C/W Q4 Q2 1X R1 Q1 10X R3 3X 2X 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 RN-8 RN-8 RT-5 TO-92 TO-92 RN-8 RN-8 RT-5 TO-92 TO-92 RN-8 RN-8 RT-5 +VOUT 7.5 A Q3 6X GND R2 2X Figure 2. 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 (mV) 250 750 500 NOTES 1 SOIC = Small Outline Integrated Circuit; 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 band gap 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. 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. C -3- TMP35/TMP36/TMP37 - Typical Performance Characteristics 2.0 1.8 1.6 a. TMP35 b. TMP36 c. TMP37 VS = 3V 100 31.6 10 3.16 1 0.32 0.1 c 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 50 a b POWER SUPPLY REJECTION - C/V OUTPUT VOLTAGE - V 0.032 0.01 20 25 0 25 50 75 TEMPERATURE - C 100 125 100 1k FREQUENCY - Hz 10k 100k TPC 1. Output Voltage vs. Temperature TPC 4. Power Supply Rejection vs. Frequency 5 4 3 5 MINIMUM SUPPLY VOLTAGE - V 4 MINIMUM SUPPLY VOLTAGE REQUIRED TO MEET DATA SHEET SPECIFICATION NO LOAD ACCURACY ERROR - C 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 TPC 2. Accuracy Error vs. Temperature TPC 5. 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 A 0.3 NO LOAD 40 a 30 0.2 0.1 SUPPLY CURRENT - 20 b 0 50 25 0 25 50 75 TEMPERATURE - C 100 125 10 50 25 0 25 50 75 TEMPERATURE - C 100 125 TPC 3. Power Supply Rejection vs. Temperature TPC 6. Supply Current vs. Temperature -4- REV. C TMP35/TMP36/TMP37 50 TA = 25C, NO LOAD 40 A 300 SUPPLY CURRENT - 400 = SHUTDOWN PIN HIGH TO LOW (3V TO 0V) 30 RESPONSE TIME - s 200 20 100 10 = SHUTDOWN PIN LOW TO HIGH (0V TO 3V) VOUT SETTLES WITHIN 1C 0 0 1 2 3 4 5 SUPPLY VOLTAGE - V 6 7 8 0 50 25 0 25 50 75 TEMPERATURE - C 100 125 TPC 7. Supply Current vs. Supply Voltage TPC 10. VOUT Response Time for Shutdown Pin vs. Temperature 50 a. V+ = 5V b. V+ = 3V NO LOAD OUTPUT VOLTAGE - V 1.0 0.8 0.6 0.4 0.2 0 1.0 0.8 0.6 0.4 b 0.2 125 0 50 0 50 100 150 200 250 TIME - s 300 350 400 450 TA = 25 C V+ AND SHUTDOWN = SIGNAL TA = 25 C V+ = 3V SHUTDOWN = SIGNAL 40 SUPPLY CURRENT - nA 30 20 a 10 0 50 25 0 25 50 75 TEMPERATURE - C 100 TPC 8. Supply Current vs. Temperature (Shutdown = 0 V) TPC 11. VOUT Response Time to Shutdown and V+ Pins vs. Time 400 110 100 90 a PERCENT OF CHANGE - % 300 RESPONSE TIME - = V+ AND SHUTDOWN PINS HIGH TO LOW (3V TO 0V) 80 70 60 50 40 30 20 10 s 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 0.5" x 0.3" Cu PCB b. TMP36 SOIC SOLDERED TO 0.6" x 0.4" Cu PCB c. TMP35 TO-92 IN SOCKET SOLDERED TO 1" x 0.4" Cu PCB 0 50 25 0 25 50 75 TEMPERATURE - C 100 125 0 0 100 200 300 TIME - sec 400 500 600 TPC 9. VOUT Response Time for V+ Power-Up/PowerDown vs. Temperature TPC 12. Thermal Response Time in Still Air REV. C -5- TMP35/TMP36/TMP37 140 120 100 a. TMP35 SOIC SOLDERED TO 0.5" x 0.3" Cu PCB b. TMP36 SOIC SOLDERED TO 0.6" x 0.4" Cu PC c. TMP35 TO-92 IN SOCKET SOLDERED TO 1" x 0.4" Cu PCB 10mV 100 90 1ms TIME CONSTANT - sec 80 VIN = 3V, 5V 60 b 40 c 20 a 0 100 200 300 400 500 AIR VELOCITY - FPM 600 700 VOLT/DIVISION 10 0% 0 TIME/DIVISION TPC 13. Thermal Response Time Constant in Forced Air TPC 15. Temperature Sensor Wideband Output Noise Voltage. Gain = 100, BW = 157 kHz 110 100 a 2400 2200 VOLTAGE NOISE DENSITY - nV/ Hz 90 80 c b VIN = 3V, 5V 2000 1800 1600 1400 1200 1000 800 600 b CHANGE - % 70 60 50 40 30 20 10 0 0 a. TMP35 SOIC SOLDERED TO 0.5" x 0.3" Cu PCB b. TMP36 SOIC SOLDERED TO 0.6" x 0.4" Cu PCB c. TMP35 TO-92 IN SOCKET SOLDERED TO 1" x 0.4" Cu PCB a 400 200 a. TMP35/36 b. TMP37 100 1k FREQUENCY - Hz 10k 10 20 30 TIME - sec 40 50 60 0 10 TPC 14. Thermal Response Time in Stirred Oil Bath TPC 16. Voltage Noise Spectral Density vs. Frequency -6- REV. C TMP35/TMP36/TMP37 APPLICATIONS SECTION Shutdown Operation 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 SOIC-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 SOIC-8, Pin 2 on the SOT-23). The shutdown response time of these temperature sensors is illustrated in TPCs 9, 10, and 11. Mounting Considerations 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: TJ = PD x (JC + CA ) + TA 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. TPCs 12 and 14 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 seconds. Basic Temperature Sensor Connections 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. 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 Figure 4 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" as are Pins 2, 3, 6, and 7 on the SOIC-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 SOIC-8 package, the SHUTDOWN pin should be connected to VS. 2.7V < Vs < 5.5V 0.1 F Vs SHDN TMP3x GND VOUT The thermal environment in which the TMP3x sensors are used determines two important characteristics: self-heating effects and thermal response time. Illustrated in Figure 3 is a thermal model of the TMP3x temperature sensors that is useful in understanding these characteristics. TJ JC PIN ASSIGNMENTS PACKAGE SOIC-8 SOT-23-5 TO-92 VS 8 2 1 GND 4 5 3 VOUT 1 1 2 SHDN 5 4 NA TC CA PD CCH CC TA Figure 4. Basic Temperature Sensor Circuit Configuration Figure 3. Thermal Circuit Model REV. C -7- TMP35/TMP36/TMP37 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 be 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 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 5b. 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. VS VS 0.1 F VOUT R1 45.3k TMP36 GND 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 5a 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 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: R1 R3 TMP 35 + VOUT = AD589 R1+ R2 R3 + R4 R2 10k VOUT @ 1mV/ F - 58 F VOUT @ -40 F = 18mV VOUT @ +257 F = 315mV Figure 5b. TMP36 Fahrenheit Thermometer Version 1 ( ) ( ) 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. VS 0.1 F VS R1 At the expense of additional circuitry, the offset produced by the circuit in Figure 5b can be avoided by using the circuit in Figure 5c. In this circuit, the output of the TMP36 is conditioned by a singlesupply, 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: R6 R4 R4 V 1+ TMP 36 - S VOUT = R5 + R6 R3 R3 2 ( ) Average and Differential Temperature Measurement TMP35/37 GND VOUT R2 VOUT AD589 1.23V R3 R4 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 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 6a and 6b demonstrate an inexpensive approach to average and differential temperature measurement. In Figure 6a, 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. Figure 5a. TMP35/TMP37 Fahrenheit Thermometers -8- REV. C 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 5c. TMP36 Fahrenheit Thermometer Version 2 The circuit in Figure 6b 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, 2.7V < +VS < 5.5V 0.1 F 7 1 3 VTEMP( AVG) @ 10mV/ C FOR TMP35/36 @ 20mV/ C FOR TMP35/36 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 0.1 F TMP36 @ T1 R1* R8 25k R2* 2 OP193 4 R5 100k 7 2 R3* R9 25k CENTERED AT 6 VOUT 0.1 F R1 300k TMP3x R6 7.5k 0.1 F OP193 3 4 TMP36 @ T2 R2 300k R7 100k TMP3x FOR R1 = R2 = R3 = R; R3 300k VTEMP( AVG) = 1 (TMP3x1 + TMP3x2 + TMP3x3) 3 R5 = R1 3 R4 = R6 R4* 1F TMP3x R4 7.5k 0 TA 125 C R5 100k R6 100k VOUT = T2 - T1 @ 10mV/ C V CENTERED AT S 2 *R1-R4, CADDOCK T914-100k-100, OR EQUIVALENT Figure 6a. Configuring Multiple Sensors for Average Temperature Measurements Figure 6b. Configuring Multiple Sensors for Differential Temperature Measurements REV. C -9- 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(R) laptop computers, the need to indicate a microprocessor overtemperature condition has grown tremendously. The circuit illustrated in Figure 7 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 8 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 ( ) Because of 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. 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, and so on. They may also be used at considerable distances 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 VREF 13 R1B 10k 3 6 4 0.1 F TMP35 R5 100k GND C1 5 2 14 INTERRUPT >80 C <80 C 3 REF191 4 6 1F R4 10k 0.1 F C1 = 1 CMP402 4 Figure 7. Pentium Overtemperature Interrupt Generator Pentium is a registered trademark of Intel Corporation. -10- REV. C 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 THERMOCOUPLE ALUMEL CU 7 P1 50k TMP35 GND OP193 3 4 R6 100k 5% VOUT 0V - 2.5V COLD JUNCTION CU R2* 102 NOTE: ALL RESISTORS 1% UNLESS OTHERWISE NOTED 0C T 250 C ISOTHERMAL BLOCK Figure 8. A Single-Supply, Type K Thermocouple Signal Conditioning Circuit with Cold-Junction Compensation Illustrated in Figure 9 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 the 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, 2-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 10. 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 R 7 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 9. A Remote, 2-Wire Boosted Output Current Temperature Sensor REV. C -11- 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 TMP3x GND VOUT 4 3 5 AD654 2 fOUT R1 RT* 5V P2 100k P1 NB: ATTA (min), fOUT = 0Hz fOUT ROFF1 470 OFFSET ROFF2 10 *RT AND 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 11 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: V - VOFFSET f OUT = TMP 10 x RT x CT SENSOR TMP35 TMP36 TMP37 RT (R1 + P1) 11.8k + 500 16.2k + 500 18.2k + 1k CT 1.7nF 1.8nF 2.1nF Figure 11. A Temperature-to-Frequency Converter ( ) 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 Figure 11 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 frequency-to-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 D1: HP5082-2810 A1: OP193 R7 100 IL Figure 10. A Temperature to 4-to-20 mA Loop Transmitter -12- REV. C TMP35/TMP36/TMP37 Driving Long Cables or Heavy Capacitive Loads Commentary on Long-Term Stability 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 12. 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 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. 0.1 F TMP3x VOUT 750 LONG CABLE OR HEAVY CAPACITIVE LOADS GND Figure 12. Driving Long Cables or Heavy Capacitive Loads REV. C -13- TMP35/TMP36/TMP37 OUTLINE DIMENSIONS 3-Pin Plastic Header-Style Package [TO-92] (TO-92) Dimensions shown in inches and (millimeters) 8-Lead Standard Small Outline Package [SOIC] Narrow Body (RN-8) Dimensions shown in millimeters and (inches) 5.00 (0.1968) 4.80 (0.1890) 8 5 4 0.135 (3.43) MIN 0.205 (5.21) 0.175 (4.45) 0.210 (5.33) 0.170 (4.32) SEATING PLANE 0.050 (1.27) MAX 4.00 (0.1574) 3.80 (0.1497) 1 6.20 (0.2440) 5.80 (0.2284) 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) COPLANARITY SEATING 0.10 PLANE 0.500 (12.70) MIN 0.019 (0.482) SQ 0.016 (0.407) 1.75 (0.0688) 1.35 (0.0532) 8 0.25 (0.0098) 0 0.19 (0.0075) 0.50 (0.0196) 0.25 (0.0099) 45 0.51 (0.0201) 0.33 (0.0130) 1.27 (0.0500) 0.41 (0.0160) 0.105 (2.66) 0.095 (2.42) 0.115 (2.92) 0.080 (2.03) 0.055 (1.40) 0.045 (1.15) COMPLIANT TO JEDEC STANDARDS MS-012AA CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN 0.115 (2.92) 0.080 (2.03) 1 2 3 0.165 (4.19) 0.125 (3.18) 5-Lead Plastic Surface-Mount Package [SOT-23] (RT-5) Dimensions shown in millimeters 2.90 BSC BOTTOM VIEW COMPLIANT TO JEDEC STANDARDS TO-226AA CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETERS DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN 5 4 1.60 BSC 1 2 3 2.80 BSC PIN 1 0.95 BSC 1.30 1.15 0.90 1.90 BSC 1.45 MAX 10 0 0.15 MAX 0.50 0.30 SEATING PLANE 0.22 0.08 0.60 0.45 0.30 COMPLIANT TO JEDEC STANDARDS MO-178AA Revision History Location 10/02--Data Sheet changed from REV. B to REV. C. Page Deleted text from Commentary on Long-Term Stability section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Update OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 -14- REV. C -15- -16- C00337-0-10/02(C) PRINTED IN U.S.A. |
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