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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 µA Quiescent Current Shutdown Current 0.5 µA Max Low Self-Heating APPLICATIONS Environmental Control Systems Thermal Protection Industrial Process Control Fire Alarms Power System Monitors CPU Thermal Management GENERAL DESCRIPTION
Low Voltage Temperature Sensor TMP35/TMP36/TMP37*
FUNCTIONAL DIAGRAM
+Vs (2.7V to 5.5V)
TMP35
SHUTDOWN
TMP36 TMP37
VOUT
PACKAGE TYPES AVAILABLE
SOT-25 (SOT23-5)
VOUT 1 +VS 2 NC 3 TOP VIEW (Not to Scale) 4 SHUTDOWN 6 GND
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 1°C at 25°C and 2°C over the 40°C to 125°C temperature range. The low output impedance of the TMP35/TMP36/ TMP37, 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 µA providing very low self-heating, less than 0.1°C in still air. In addition, a shutdown function is provided to cut supply current to less than 0.5 µA. The TMP35 is functionally-compatible with the LM35/LM45 and provides a 250 mV output at 25°C. The TMP35 reads temperatures from 10°C to 125°C. The TMP36 is specified from 40°C to 125°C, provides a 750 mV output at 25°C and operates to 125°C from a single 2.7 V supply. Both the TMP35 and TMP36 have an output scale factor of 10 mV/°C. The TMP37 is intended for applications over the range 5°C to 100°C, and provides an output scale factor of 20 mV/°C. The TMP37 provides a 500 mV output at 25°C. Operation extends to 150°C 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-25 surface mount packages.
* Patent pending.
NC = NO CONNECT
SO-8
VOUT 1 NC 2 8 +VS
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
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Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. © Analog Devices, Inc., 1996 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
TMP35/TMP36/TMP37F/GSPECIFICATIONS 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 Scale Factor, TMP37 Load Regulation Power Supply Rejection Ratio 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 Guaranteed but not tested. 2 Does not consider errors caused by self-heating Specifications subject to change without notice.
(VS =
2.7 V to 5.5 V,
Typ 1 1 2 2 10 10 20 20 1 30 50 0.5 0.4
40°C
TA
125°C
Units °C °C °C °C mV/°C mV/°C mV/°C mV/°C m°C/µA m°C/V m°C/V °C °C V mV mV mV mV mV µA µA pF ms
Symbol
Conditions TA = 25°C TA = 25°C Over Rated Temperature Over Rated Temperature 125°C 10°C TA 125°C 40°C TA 85°C 5°C TA 100°C 5°C TA 3.0 V VS 5.5 V 0 µA IL 50 µA TA = 25°C 3.0 V VS 5.5 V TA = 150°C for 1 kHrs
Min
Max 2 3 3 4 9.8/ 10.2 9.8/ 10.2 19.6/ 20.4 19.6/ 20.4 20 100
PSRR PSRR
VIH VIL
VS = 2.7 V VS = 5.5 V TA = TA = TA = 25°C 25°C 25°C
1.8 400 250 750 500 100 0 10,000 0.5 2,000 50 250 1
IL ISC CL
Note 1 No oscillations1 Output within 1°C 100 k //100 pF Load1
1,000
VS ISY (ON) ISY (OFF)
2.7 Unloaded Unloaded 0.01
5.5 50 0.5
V µA µA
2
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TMP35/TMP36/TMP37 WAFER TEST LIMITS (V
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)
S
=
5 V, GND = O V, TA =
Symbol
25°C, unless otherwise noted.)
Conditions TA = 25°C 2.7 V VS VS = 2.7 V VS = 5.5 V TA = 25°C TA = 25°C TA = 25°C VS = 5.5 V Output within 1°C 100 k//100 pF Load1 2.7 Unloaded at Unloaded at 5V 5V Min Typ Max 2 5.5 V 1.8 400 250 750 500 0.5 250 1 30 Units °C m°C/V V mV mV mV mV µA msec
PSRR VIH VIL
ISC
V ISY (ON) ISY (OFF)
5.5 50 0.5
V µA µA
NOTE 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. 1Guaranteed but not tested.
DICE CHARACTERISTICS
Die Size 0.027 0.030 inch, 810 sq. mils (0.685 0.762 mm, 0.522 sq. mm) Transistor Count: 25 Substrate is connected to V S
1
4
1. V OUT 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
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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 . . . . . . . . . . 55°C to 150°C Dice Junction Temperature . . . . . . . . . . . . . . . . . . . . . 175°C Storage Temperature Range . . . . . . . . . . . . 65°C to 160°C Lead Temperature (Soldering, 60 sec) . . . . . . . . . . . . 300°C Package Type TO-92 (T9 suffix) SO-8 (S suffix) SOT-25 (RT suffix) JA 1621 1581 3001 JC 120 43 180 Units °C/W °C/W °C/W
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 µA. 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:
VBE = VT
+VS
ln
AE,Q1 AE,Q2
NOTES 1 JA is specified for device in socket (worst case conditions). 2 JA is specified for device mounted on PCB.
SHDN 25µA
*CAUTION
3X
2X
1. 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. 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.
ORDERING GUIDE
VOUT
Q2 1X Q4 Q1 10X R3 R2 R1
7.5 µA Q3 6X GND 2X
Figure 1. Temperature Sensor Simplified Equivalent Circuit
Model TMP35FT9 TMP35GT9 TMP35FS TMP35GS TMP35GRT1 TMP36FT9 TMP36GT9 TMP36FS TMP36GS TMP36GRT1 TMP37FT9 TMP37GT9 TMP37FS TMP37GS TMP37GRT1
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 Temp. Range 10°C to 10°C to 10°C to 10°C to 10°C to 40°C to 40°C to 40°C to 40°C to 40°C to 5°C to 5°C to 5°C to 5°C to 5°C to 125°C 125°C 125°C 125°C 125°C 125°C 125°C 125°C 125°C 125°C 100°C 100°C 100°C 100°C 100°C
Package TO-92 TO-92 SO-8 SO-8 SOT-25 TO-92 TO-92 SO-8 SO-8 SOT-25 TO-92 TO-92 SO-8 SO-8 SOT-25
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
NOTE 1 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 µA.
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TMP35/TMP36/TMP37
2 a. TMP35 1.8 1.6 OUTPUT VOLTAGE Volts 1.4 1.2 1 0.8 0.6 0.4 0.2 0 50 a c. TMP37 VS = 3V b c POWER SUPPLY REJECTION °C/V b. TMP36 31.6 10 3.16 1 0.32 0.1 100
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 2 1 0 1 b 2 3 4 5 0 20 40 60 80 100 TEMPERATURE °C 120 140 c a a. MAXIMUM LIMIT ( G GRADE ) b. TYPICAL ACCURACY ERROR c. MINIMUM LIMIT ( G GRADE ) MINIMUM SUPPLY VOLTAGE Volts
5
4
MINIMUM SUPPLY VOLTAGE REQUIRED TO MEET DATA SHEET SPECIFICATION NO LOAD
3 b 2 a
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
60 a. V+ = 5V b. V+ = 3V 50 SUPPLY CURRENT µA NO LOAD 40 a 30
POWER SUPPLY REJECTION °C/V
0.3
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
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5
TMP35/TMP36/TMP37
50 TA = +25°C, NO LOAD 40 SUPPLY CURRENT µA 300 30 RESPONSE TIME µS 400 = SHUTDOWN PIN HIGH TO LOW ( 3V TO 0V )
200
20
100 10 = SHUTDOWN PIN LOW TO HIGH ( 0V TO 3V ) VOUT SETTLES WITHIN ±1°C 0 1 2 3 4 5 6 SUPPLY VOLTAGE Volts 7 8 0 50 25 0 25 50 75 TEMPERATURE °C 100 125
0
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 NO LOAD 30
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 µs 300 350 400 450 TA = 25°C V+ & SHUTDOWN = SIGNAL TA = 25°C V+ = 3V SHUTDOWN = SIGNAL
40 SUPPLY CURRENT nA
20 a 10
0
50
25
0
25 50 75 TEMPERATURE °C
100
Figure 9. Supply Current vs. Temperature (Shutdown = 0 V)
Figure 12. VOUT Response Time to Shutdown and V Pins vs. Time
400
110 a 100 90 PERCENT OF CHANGE % VIN = +3V, +5V 80 70 60 50 40 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 c b
300 RESPONSE TIME µS = V+ AND SHUTDOWN PINS HIGH TO LOW ( 3V TO 0V )
200 = V+ AND SHUTDOWN PINS LOW TO HIGH ( 0V TO 3V ) VOUT SETTLES WITHIN ±1°C 100
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 vs. Temperature
Power Up/Down
Figure 13. Thermal Response Time in Still Air
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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 c. TMP35 TO-92 IN SOCKET SOLDERED TO 1" x .4" Cu PCB VOLT/DIVISION
100 90
10mV
1mS
80 VIN = +3V, +5V 60 b 40 c 20
10 0%
TIME sec 0 0 100 200 a 300 400 500 AIR VELOCITY FPM 600 700 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 % 70 60 50 40 b
a
2400 2200 2000 c VOLTAGE NOISE DENSITY nV / Hz VIN = +3V, +5V 1800 1600 1400 1200 1000 800 600 a 400 200 0 10 a. TMP35/36 b. TMP37 100 1K FREQUENCY Hz 10K b
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
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 µA, maximum. This feature, available in only the SO-8 and the SOT-25 packages, is TTL/CMOS level compatibleprovided 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-25). 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 40°C to 125°C. Properly cemented or glued to the surface of the medium, these sensors will be within 0.01°C 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 non-conductive, is recommended under typical mounting conditions.
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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 dips, 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 which is useful in understanding these characteristics.
Tj
JC
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-25, Pin 3 is labeled as "NC" as well 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-25 or the SO-8 package, the SHUTDOWN pin should be connected to VS.
2.7V VS 5.5V 0.1µF
TC
VS
CA
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 120°C/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
JC
CA
SO-8 SOT-25 TO-92
Figure 19. Basic Temperature Sensor Circuit Configuration
TA
Thus, the die temperature rise of a TMP35 "RT" package mounted into a socket in still air at 25°C and driven from a 5 V supply is less than 0.04°C. 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 that is 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 to be 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 µF 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 µF) placed across the 0.1 µF 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 read Fahrenheit temperatures directly. 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 41°F to 257°F with an output transfer characteristic of 1 mV/°F using the TMP35 and from 41°F to 212°F 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 4 resistors whose values for each sensor are shown in the figure table. The scaling of the
8
TMP35/TMP36/TMP37
output resistance levels was to ensure minimum output loading on the temperature sensors. An generalized expression for the circuit's transfer equation is given by:
VOUT = R1 R1 R2 TMP35 R3 R3 R4 AD589
0.1µF VS VS VOUT
TMP36
GND
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 in 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
R2 10k
VOUT @ 1mV/ °F - 58°F
VOUT @ -40°F = 18mV 0.1µF VS VOUT @ 257°F = 315mV
TMP35/37
GND
VOUT
R1
Figure 20b. TMP36 Fahrenheit Thermometer Version 1
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 40°F and 257°F, the output of the circuit reads 40 mV to 257 mV. A general expression for the circuit's transfer equation is given by:
VOUT = R6 R5 R6 1 R4 TMP36 R3 R4 R3 VS 2
SENSOR TMP35 TMP37
TCVOUT 1mV/°F 2mV/°F
R1 (k) 45.3 45.3
R2 (k) 10 10
R3 (k) 10 10
R4 (k) 374 182
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 (58°F) offset in the output voltage. For example, the output voltage of the circuit would read 18 mV, if the TMP36 is placed in 40°F ambient environment, and 315 mV at 257°F.
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 so 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.
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TMP35/TMP36/TMP37
+3V
R1 50k R3 C1 + 10µF 8 VS + 10µF/0.1µF VOUT R5 2
OP193
R4
R2 50k
0.1µF
VOUT @ 1mV/°F 6 -40°F TA 257°F
TMP36
GND
3
4 R6 8 1 ELEMENT R3 R4 R5 R6 TMP36 258.6k 10k 47.7k 10k NC 2 10µF + 4 3 7 NC 5 -3V 10µF
ADM660
6
+
Figure 20c. TMP36 Fahrenheit Thermometer Version 2
2.7V +VS 5.5V VTEMP(AVG) @ 10mV/° C
0.1µF 7 1 3
OP193
shown in the figure. Using the TMP35, the output voltage of the circuit is scaled by 10 mV/°C and, using the TMP37, the output voltage can be scaled by 20 mV/°C. To minimize error in the difference between the two measured temperatures, a common, readily available thin-film resistor network is used for R1R4.
2.7V < VS < 5.5V
2
4 R1 100k R1* R2*
TMP3x
FOR R1 = R2 = R3 =R; VTEMP(AVG) = 1 (TMP3X1 + TMP3X2 + TMP3X3) 3 R2 100k
0.1µ
TMP3x @T1
TMP3x
VTEMP(EFF) 7 2 R3 100k
0.1µF
6 0.1µ
VOUT
TMP3x
TMP3x @T2
R3*
3
OP193
4
R4*
Figure 21a. Configuring Multiple Sensors for Average Temperature Measurements
R7 100k 1µF
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, as
R5 100k
R6 100k
VOUT = T2 T1 @ 10mV/ ° C CENTERED AT VS
* R1-R4, CADDOCK T914100k100, OR EQUIVALENT
2
Figure 21b. Configuring Multiple Sensors for Differential Temperature Measurements
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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 so as to produce a logic HIGH interrupt signal if the microprocessor temperature exceeds 80°C. This 80°C trip point was chosen arbitrarily (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 5°C 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 5°C (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 = R2 VLOGIC SWING, CMP402
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 0°C and 250°C. The circuit operates from single 13.3 V to 15.5 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 µV/°C; therefore, at the cold junction, the TMP35 with an temperature coefficient of 10 mV/°C is used with R1 and R2 to introduce an opposing cold-junction temperature coefficient of 41 µV/°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 20°C to 50°C. Over a 250°C 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 0°C 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 µF capacitor is used across R4. *Pentium TM
is a trademark of Intel Corporation.
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. Furthermore, they may 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 0.1µF 3 VOUT R1A 10k GND 0.1µF 2 R3 16k 6 VREF + 4 1µF R4 10k CL 1000pF R1B 10k 6 5 4 2
VS 0.1µF
TMP35
C1
14 13 80°C
INTERRUPT
80°C
REF191
3 0.1µF
1 C1 = CMP402 4
Figure 22. Pentium Over-Temperature Interrupt Generator
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TMP35/TMP36/TMP37
3.3V < VS < 5.5V
VS VOUT R3 10M 5% R4 4.99k R5* 1.21M 0.1µF GND R1* 24.9k 7 2 6 CHROMEL + COLD JUNCTION CU 3
OP193
P1 50k
0.1µF
TMP35
VOUT 0 - 2.5V R6 100k 5%
TYPE K THERMO COUPLE
4
ALUMEL
CU
NOTE: ALL RESISTORS 1% UNLESS OTHERWISE NOTED R2* 102
0°C
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 for 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 420 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 which 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 REF193's +3 V output. 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:
IOUT = 1 R7 TMP3x R3 R1 VREF R3 R2
R1 4.7k 2N2907 0.1µF VS VOUT
+5V
VOUT
TMP3X
0.01µF GND
R3
For each of the three temperature sensors, the table below illustrates the values for each of the components, P1, P2, and R1R4:
Table II. Circuit Element Values for Loop Transmitter
R2
TWISTED PAIR BELDEN TYPE 9502 OR EQUIVALENT
Sensor TMP35 TMP36 TMP37
R1() 97.6 k 97.6 k 97.6 k
P1() 5k 5k 5k
R2() 1.58 M 931 k 10.5 k
P2() R3() 100 k 50 k 500 140 k 97.6 k 84.5 k
R4() 56.2 k 47 k 8.45 k
SENSOR R2 TMP35 TMP36 TMP37
R3
634 634 887 887 1k 1k
Figure 24. A Remote, Two-Wire Boosted Output Current Temperature Sensor
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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 0.1µF VS VOUT 4 3 GND 5 8 6 7 1 CT* RPU 5k
10µF/0.1µF
TMP3x
AD654
2
fout
RT* +5V
{
R1 NB : AT TA (min), fout = 0Hz P1 fout 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. Theses 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:
fOUT = VTMP 10 VOFFSET RT CT
P2 100k
ROFF1 470
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
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 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* 1µF 4 VLOOP +9V TO +18V
VS R1*
P2* 4mA ADJUST 3 P1* 20mA ADJUST D1 R3* R4* 2 7 A1 4
0.1µF R6 100k
TMP3x TMP3X
VOUT GND
Q1 2N1711 VOUT
R5 100k
RL 250
* SEE TEXT FOR VALUES
D1 : HP50822810 A1 : OP193
R7 100
IL
Figure 25 A Temperature to 4-to-20 mA Loop Transmitter
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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. Furthermore, since the temperature sensor is likely to be used in environments where the ambient noise level can be very high, this resistors helps to prevent rectification by the devices of the high frequency noise. The combination of the this resistor and the supply bypass capacitor offers the best protection.
+VS
For example, if the desired operating temperature of an IC is 25°C and has been subjected to test temperature of 150°C, the acceleration factor is:
F = 3.23 10-4
With this background information, the TMP3x family's longterm stability can be mapped to what its equivalent observed shift would be at TA = 25°C. As quoted in the data sheet, the long-term stability of these temperature sensors after 1000 hours at 150°C is 0.4°C. This shift is equivalent to 0.01°C/day at TJ = 150°C. To determine what the observed shift would be at TA = 25°C is a matter of applying the acceleration factor calculated above to this result:
0.01°C/day 3.23 10-4 0.003 m°C/day @ 25°C
0.1µF
TMP3x
VOUT
750
LONG CABLE OR HEAVY CAPACITIVE LOADS
Thus, if any of the TMP3x devices were to be used at 25°C, then the observed shift would be no more than 0.003 m°C per day, or 0.1 m°C per month. Calculating the observed shift for any other operating temperature is simply a matter of calculating a new acceleration factor.
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 (25°C) 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 125°C and 150°C) 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 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., 0.4°C after 1000 hours at TJ = 150°C) to an observed shift in that parameter at 25°C. For any semiconductor device, the acceleration factor is expressed as:
F = exp Ea k 1 T1 1 T2
where F = Calculated acceleration factor; E a = activation energy in eV = 0.7 eV; k = Boltzmann's constant = 8.63 x 10-5 eV/K; T1 = Test temperature in Kelvin, TJ = 150°C = 423.15 K; and T2 = Desired operating temperature in Kelvin, TJ = 25°C = 298.15 K
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OUTLINE DIMENSIONS
Dimensions shown in inches and (mm). Note SOT-25 package shown only in mm.
TO-92
0.205 (5.20) 0.175 (4.96) 0.1968 (5.00) 0.1890 (4.80)
8-Pin SOIC
0.135 (3.43) MIN
0.210 (5.33) 0.170 (4.38) SEATING PLANE 0.500 (1.27) MAX
0.1574 (4.00) 0.1497 (3.80)
8 1
5 4
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)
0.0196 (0.50) 0.0099 (0.25)
45°
0.500 (12.70) MIN
0.019 (0.482) 0.016 (0.407)
SQUARE
SEATING PLANE
0.0500 0.0192 (0.49) (1.27) 0.0138 (0.35) BSC
0.0098 (0.25) 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) (2.700) (3.100) (0.950) REF
SOT-25
0.105 (2.66) 0.080 (2.42)
1
2
3
0.165 (4.19) 0.125 (3.94) (1.500) (1.800)
BOTTOM VIEW
(2.500) (3.000)
(1.900) REF (0.900) (1.300) (0.300) (0.500) SEATING PLANE (0.090) (0.200)
(0.000) (0.150)
(0.00°) (10.0°) (0.100) (0.600)
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