a
Low Voltage Temperature Sensors
TMP35/TMP36/TMP37
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)
2C Accuracy Over Temperature (Typ)
0.5C Linearity (Typ)
Stable with Large Capacitive Loads
Specified –40C to +125C, Operation to +150C
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
PRODUCT DESCRIPTION
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, 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 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. 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 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-23 surface mount packages.
FUNCTIONAL BLOCK DIAGRAM
+Vs (2.7V to 5.5V)
TMP35/
SHUTDOWN
TMP36/
TMP37
V
OUT
PACKAGE TYPES AVAILABLE
RT-5 (SOT-23)
V
1
OUT
+V
2
S
3
NC
NC = NO CONNECT
TOP VIEW
(Not to Scale)
GND
5
4
SHUTDOWN
SO-8
1
V
OUT
2
NC
3
NC
4
GND
NC = NO CONNECT
TOP VIEW
(Not to Scale)
8
+V
S
7
NC
6
NC
5
SHUTDOWN
TO-92
2
1 3
BOTTOM VIEW
(Not to Scale)
PIN 1, +Vs; PIN 2, V
; PIN 3, GND
OUT
REV. B
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.
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 © Analog Devices, Inc., 2001
(VS = 2.7 V to 5.5 V, –40C ≤ TA ≤ +125C unless
1
TMP35/TMP36/TMP37–SPECIFICATIONS
otherwise noted)
Parameter Symbol Conditions Min Typ Max Unit
ACCURACY
TMP35/TMP36/TMP37F TA = 25°C ±1 ±2 °C
TMP35/TMP36/TMP37G T
= 25°C ±1 ±3 °C
A
TMP35/TMP36/TMP37F Over Rated Temperature ±2 ±3 °C
TMP35/TMP36/TMP37G Over Rated Temperature ±2 ±4 °C
Scale Factor, TMP35 10°C ≤ T
Scale Factor, TMP36 –40°C ≤ T
Scale Factor, TMP37 5°C ≤ T
5°C ≤ T
3.0 V ≤ +V
Load Regulation 0 µA ≤ I
–40°C ≤ T
–105°C ≤ T
Power Supply Rejection Ratio PSRR T
= 25°C 30 100 m°C/V
A
3.0 V ≤ +V
≤ 125°C 10 9.8/10.2 mV/°C
A
≤ +125°C 10 9.8/10.2 mV/°C
A
≤ 85°C 20 19.6/20.4 mV/°C
A
≤ 100°C 20 19.6/20.4 mV/°C
A
≤ 5.5 V
S
≤ 50 µA
L
≤ +105°C620m°C/µA
A
≤ +125°C2560m°C/µA
A
≤ 5.5 V 50 m°C/V
S
Linearity 0.5 °C
Long-Term Stability TA = +150°C for 1 kHrs 0.4 °C
SHUTDOWN
Logic High Input Voltage V
Logic Low Input Voltage V
IH
IL
VS = 2.7 V 1.8 V
VS = 5.5 V 400 mV
OUTPUT
TMP35 Output Voltage TA = 25°C 250 mV
TMP36 Output Voltage T
TMP37 Output Voltage T
= 25°C 750 mV
A
= 25°C 500 mV
A
Output Voltage Range 100 2000 mV
Output Load Current I
Short-Circuit Current I
Capacitive Load Driving C
Device Turn-On Time Output within ±1°C 0.5 1 ms
L
SC
Note 2 250 µA
L
No Oscillations
100 kΩ100 pF Load
2
2
050µA
1000 10000 pF
POWER SUPPLY
Supply Range +V
Supply Current I
Supply Current (Shutdown) I
NOTES
1
Does not consider errors caused by self-heating.
2
Guaranteed but not tested.
3
See Figure 1.
Specifications subject to change without notice.
S
SY (ON)
SY (OFF)
Unloaded 50 µA
Unloaded 0.01 0.5 µA
2.7 5.5 V
50
40
30
20
LOAD REG – mC/A
10
0
–50
0 50 100 150
TEMPERATURE – C
Figure 1. Load Reg vs. Temperature (m°C/µA)
–2–
REV. B
TMP35/TMP36/TMP37
WARNING!
ESD SENSITIVE DEVICE
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 V
Shutdown Pin . . . . . . . . . . . . . . GND
Output Pin . . . . . . . . . . . . . . . . . . . . . . GND ⱕ V
≤
SHUTDOWN ≤ +V
ⱕ +V
OUT
S
S
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
*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
JA
JC
Units
TO-92 (T9 Suffix) 162 120 °C/W
SO-8 (S Suffix) 158 43 °C/W
SOT-23 (RT Suffix) 300 180 °C/W
θJA is specified for device in socket (worst-case conditions).
ORDERING GUIDE
Accuracy Linear
at 25C Operating Package
Model (C max) Temperature Range Options
1
TMP35FT9 ±2.0 10°C to 125°C TO-92
TMP35GT9 ±3.0 10°C to 125°C TO-92
TMP35FS ±2.0 10°C to 125°C SO-8
TMP35GS ± 3.0 10°C to 125°C SO-8
TMP35GRT2±3.0 10°C to 125°C RT-5
TMP36FT9 ±2.0 –40°C to +125°C TO-92
TMP36GT9 ±3.0 –40°C to +125°C TO-92
TMP36FS ±2.0 –40°C to +125°C SO-8
TMP36GS ± 3.0 –40°C to +125°C SO-8
TMP36GRT2±3.0 –40°C to +125°C RT-5
TMP37FT9 ±2.0 5°C to 100°C TO-92
TMP37GT9 ±3.0 5°C to 100°C TO-92
TMP37FS ±2.0 5°C to 100°C SO-8
TMP37GS ± 3.0 5°C to 100°C SO-8
TMP37GRT2±3.0 5°C to 100°C RT-5
NOTES
1
SO = Small Outline; RT = Plastic Surface Mount; TO = Plastic.
2
Consult factory for availability.
FUNCTIONAL DESCRIPTION
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 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 V
and Q2’s VBE are not equal
BE
by the following relationship:
A
7.5A
Q2
1X
E,Q1
A
E,Q2
25A
3X
2X
R1
R3
R2
2X
+V
SHDN
+V
OUT
GND
∆VBE=VT× ln
S
Q4
Q1
10X
Q3
6X
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 V
an offset term in V
. Table I summarizes the differences
OUT
BE
as
between the three temperature sensors’ output characteristics:
Table I. TMP3x Output Characteristics
Offset Output Voltage Output Voltage
Sensor Voltage (V) Scaling (mV/C) @ 25C
TMP35 0 10 250 mV
TMP36 0.5 10 750 mV
TMP37 0 20 500 mV
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.
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.
REV. B
–3–
TMP35/TMP36/TMP37
– Typical Performance Characteristics
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
OUTPUT VOLTAGE – V
0.4
0.2
50 25 0 25 50 75 100 125
a. TMP35
b. TMP36
c. TMP37
= 3V
V
S
0
TEMPERATURE – C
c
a
TPC 1. Output Voltage vs. Temperature
5
4
3
a. MAXIMUM LIMIT ( G GRADE )
2
1
0
1
2
ACCURACY ERROR – C
3
4
5
0 20 40 60 80 100 120 140
a
b. TYPICAL ACCURACY ERROR
c. MINIMUM LIMIT ( G GRADE )
b
c
TEMPERATURE – C
TPC 2. Accuracy Error vs. Temperature
100
31.6
10
b
3.16
1
0.32
0.1
POWER SUPPLY REJECTION – C/V
0.032
0.01
20 100k100 1k 10k
FREQUENCY – Hz
TPC 4. Power Supply Rejection vs. Frequency
5
MINIMUM SUPPLY VOLTAGE REQUIRED TO MEET
4
DATA SHEET SPECIFICATION
NO LOAD
3
b
2
1
MINIMUM SUPPLY VOLTAGE – V
a. TMP35/ TMP36
b. TMP37
0
50 12525 0 25 50 75 100
TEMPERATURE – C
a
TPC 5. Minimum Supply Voltage vs. Temperature
0.4
V+ = 3V to 5.5V, NO LOAD
0.3
0.2
0.1
POWER SUPPLY REJECTION – C/V
0
50 12525 0 25 50 75 100
TEMPERATURE – C
TPC 3. Power Supply Rejection vs. Temperature
–4–
60
a. V+ = 5V
50
40
30
SUPPLY CURRENT – A
20
10
b. V+ = 3V
NO LOAD
a
50 12525 0 25 50 75 100
TEMPERATURE – C
TPC 6. Supply Current vs. Temperature
b
REV. B
TMP35/TMP36/TMP37
50
TA = 25°C, NO LOAD
40
30
20
SUPPLY CURRENT – A
10
0
07123456
SUPPLY VOLTAGE – V
8
TPC 7. Supply Current vs. Supply Voltage
50
a. V+ = 5V
b. V+ = 3V
40
NO LOAD
30
20
SUPPLY CURRENT – nA
10
0
50 12525 0 25 50 75
TEMPERATURE – C
a
b
100
TPC 8. Supply Current vs. Temperature (Shutdown = 0 V)
400
= SHUTDOWN PIN
HIGH TO LOW (3V TO 0V)
300
200
RESPONSE TIME – s
100
0
50 12525 0 25 50 75
TPC 10. V
Response Time for Shutdown Pin vs.
OUT
TEMPERATURE – C
= SHUTDOWN PIN
LOW TO HIGH (0V TO 3V)
SETTLES WITHIN ±1°C
V
OUT
Temperature
1.0
0.8
0.6
0.4
0.2
0
1.0
0.8
0.6
OUTPUT VOLTAGE – Volts
0.4
0.2
0
50 2500 10050 150 200 300 350 400 450
TPC 11. V
Response Time to Shutdown and V+
OUT
= 25°C
T
A
V+ = 3V
SHUTDOWN =
SIGNAL
T
= 25°C
A
V+ AND SHUTDOWN =
SIGNAL
TIME – µs
Pins vs. Time
100
400
300
200
RESPONSE TIME – s
100
0
50 12525 0 25 50 75
TPC 9. V
Response Time for V+ Power-Up/Power-
OUT
Down vs. Temperature
REV. B
= V+ AND SHUTDOWN PINS
HIGH TO LOW (3V TO 0V)
= V+ AND SHUTDOWN PINS
LOW TO HIGH (0V TO 3V)
SETTLES WITHIN ±1°C
V
OUT
TEMPERATURE – C
100
–5–
110
100
90
80
70
60
50
40
30
PERCENT OF CHANGE – %
20
10
0
0
a
b
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
100
c
200 300 400 500 600
TIME – sec
VIN = 3V, 5V
TPC 12. Thermal Response Time in Still Air
TMP35/TMP36/TMP37
140
a. TMP35 SOIC SOLDERED TO 0.5" x 0.3" Cu PCB
120
100
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
80
60
40
TIME CONSTANT – sec
20
0
0 100 200 300 400 500 600
VIN = +3V, +5V
b
c
a
700
AIR VELOCITY – FPM
TPC 13. Thermal Response Time Constant in Forced Air
110
100
90
80
70
60
50
CHANGE – %
40
30
20
10
a
c
b
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
10
0
VIN = +3V, +5V
20 30 40 50 60
TIME – sec
TPC 14. Thermal Response Time in Stirred Oil Bath
VOLT/DIVISION
10
0%
TIME/DIVISION
TPC 15. Temperature Sensor Wideband Output
Noise Voltage. Gain = 100, BW = 157 kHz
2400
2200
2000
1800
1600
1400
1200
1000
800
600
400
VOLTAGE NOISE DENSITY – nV/ Hz
a. TMP35/36
b. TMP37
200
0
10 10k100 1k
FREQUENCY – Hz
b
a
TPC 16. Voltage Noise Spectral Density vs. Frequency
–6–
REV. B
TMP35/TMP36/TMP37
TP T
D C CA AJJ
=× +
()
+
θθ
APPLICATIONS SECTION
Shutdown Operation
All TMP3x devices include a shutdown capability that reduces
the power supply drain to less than 0.5 µA, 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 V
is connected. This permits the
IN
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 V
(Pin 8 on the SO-8, Pin 2 on the SOT-23).
IN
The shutdown response time of these temperature sensors is
illustrated in TPCs 9, 10, and 11.
Mounting Considerations
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 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
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.
T
J
T
JC
C
CA
In the TO-92 package, the thermal resistance junction-to-case,
θ
, is 120°C/W. The thermal resistance case-to-ambient, θCA, is
JC
the difference between θ
and θJC, and is determined by the
JA
characteristics of the thermal connection. The temperature
sensor’s power dissipation, represented by P
, is the product of
D
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:
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, C
thermal capacity of the case, C
, and the case, CC. The
CH
, varies with the measurement
C
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. TPC 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
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” 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 V
.
S
2.7V < Vs < 5.5V
0.1F
V
s
V
S
TMP3x
GND
GND
V
OUT
SHDN
PIN ASSIGNMENTS
PACKAGE
SO-8 8 4 1 5
SOT-23-5 2 5 1 4
TO-92 1 3 2 NA
V
OUT
SHDN
P
D
Figure 3. TMP3x Thermal Circuit Model
REV. B
C
CH
C
C
T
Figure 4. Basic Temperature Sensor Circuit Configuration
A
–7–
TMP35/TMP36/TMP37
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 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 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 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
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 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:
V
OUT
=
R1
R1+ R2
TMP 35
()
+
R3 + R4
R3
AD589
()
where: TMP35 = Output voltage of the TMP35, or the TMP37,
at the measurement temperature, T
, and
M
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.
V
TMP35/37
AD589
1.23V
S
V
GND
S
TCV
OUT
V
OUT
R1 (k)
R2 (k)R3 (k)R4 (k)
R1
R2
V
OUT
R3
R4
0.1F
PIN ASSIGNMENTS
SENSOR
TMP35 1mV/F 45.3 10 10 374
TMP37 2mV/F 45.3 10 10 182
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 (58°F) offset
in the output voltage. For example, the output voltage of the
circuit would read 18 mV, were the TMP36 placed in –40°F
ambient environment, and 315 mV at 257°F.
V
S
V
S
V
GND
OUT
R1
45.3k
R2
10k
V
@ –40F = 18mV
OUT
V
@ 257F = 315mV
OUT
@ 1mV/F – 58F
V
OUT
0.1F
TMP36
Figure 5b. TMP36 Fahrenheit Thermometer Version 1
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 –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:
OUT
=
R5+ R6
V
R6
R4
1+
TMP 36
()
R3
V
R4
R3
S
2
−
Average and Differential Temperature Measurement
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. B
10F/0.1F
TMP36
@ T1
0.1F
0.1F
2
3
4
6
7
OP193
1F
V
OUT
R3*
R4*
R2*R1*
2.7V < V
S
< 5.5V
TMP36
@ T2
R5
100k
R6
100k
V
OUT
= T2 – T1 @ 10mV/ C
V
S
2
*R1–R4, CADDOCK T914–100k–100, OR EQUIVALENT
0.1F
R7
100k
R8
25k
R9
25k
0 ⱕ TA ⱕ 125 C
CENTERED AT
CENTERED AT
V
TMP36
GND
S
V
ELEMENT
R2
R4
R5
R6
50k
50k
OUT
+3V
R1
R2
TMP36
258.6k
10k
47.7k
10k
10F
C1
NC
10F
R3 R4
R5
R6
8
1
2
ADM660
4
3
5
6
7
Figure 5c. TMP36 Fahrenheit Thermometer Version 2
TMP35/TMP36/TMP37
0.1F
8
2
V
@ 1mV/ F
OP193
3
4
6
–3V
10F
NC
OUT
–40F ⱕ TA ⱕ 257 F
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,
< 5.5V
2.7V < +V
S
0.1F
V
7
2
OP193
3
4
TMP3x
TMP3x
TMP3x
Figure 6a. Configuring Multiple Sensors for Average
Temperature Measurements
R1
300k
R2
300k
R3
300k
R4
7.5k
FOR R1 = R2 = R3 = R;
V
R4 = R6
TEMP(AVG)
R1
R5 =
3
TEMP(AVG)
@ 10mV/ C FOR TMP35/36
@ 20mV/ C FOR TMP35/36
1
R5
100k
R6
7.5k
= 1 (TMP3x1 + TMP3x2+ TMP3x3)
3
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.
Figure 6b. Configuring Multiple Sensors for Differential
Temperature Measurements
REV. B
–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 laptop computers, the
need to indicate a microprocessor over-temperature 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 80°C. This
80°C 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 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 kΩ and R2 is set to 1 MΩ. An expression for this circuit’s
hysteresis is given by:
R1
V
=
HYS
V
()
LOGIC SWING, CMP402
R2
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.
3.3V
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 0°C and 250°C. 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 µV/°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 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 kΩ
sets R5 equal to 1.22 MΩ. Since the closest 1% value for R5 is
1.21 MΩ, a 50 kΩ 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
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.
V
S
V
GND
OUT
3
R5
100k
REF191
2
4
0.1F
TMP35
Figure 7. Pentium Over-Temperature Interrupt Generator
Pentium is a registered trademark of Intel Corporation.
10k
0.1F
6
R1A
1F
1
C1 = CMP402
4
C
1000p
F
R3
16k
L
–10–
R1B
10k
R4
10k
R2
1M
0.1F
3
6
5
V
REF
0.1F
4
C1
13
2
14
<80C
INTERRUPT
>80C
REV. B
3.3V < V
< 5.5V
S
TMP35/TMP36/TMP37
TYPE K
THERMOCOUPLE
0.1F
CHROMEL
ALUMEL
0C ⱕ T ⱕ 250C
V
S
TMP35
GND
COLD
JUNCTION
ISOTHERMAL
BLOCK
V
OUT
R1*
24.9k
CU
CU
R2*
102
R3
R4
10M
4.99k
5%
NOTE: ALL RESISTORS 1%
UNLESS OTHERWISE NOTED
2
3
7
OP193
R5*
1.21M
0.1F
6
4
50k
R6
100k
5%
P1
0 – 2.5V
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 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 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:
TMP 3x × R3
I
OUT
1
R 7
×
R1
=
V
× R3
REF
+
R2
For each of the three temperature sensors, the table below illustrates the values for each of the components, P1, P2 and R1–R4:
0.1F
0.01F
R1
4.7k
TMP3x
5V
2N2907
V
S
V
OUT
V
OUT
R3
V
OUT
GND
SENSOR R2 R3
TMP35 634 634
TMP36 887 887
TMP37 1k 1k
R2
TWISTED PAIR
BELDEN TYPE 9502
OR EQUIVALENT
Figure 9. A Remote, Two-Wire Boosted Output Current
Temperature Sensor
REV. B
Table II. Circuit Element Values for Loop Transmitter
Sensor R1() P1() R2() P2() R3() R4()
TMP35 97.6 k 5 k 1.58 M 100 k 140 k 56.2 k
TMP36 97.6 k 5 k 931 k 50 k 97.6 k 47 k
TMP37 97.6 k 5 k 10.5 k 500 84.5 k 8.45 k
–11–
TMP35/TMP36/TMP37
TMP3x
V
S
GND
6
4
2
3
7
8
5
1
AD654
V
OUT
10F/0.1F
5V
P2
100k
R
OFF1
470
f
OUT
OFFSET
R
OFF2
10
R1
P1
R
T
*
0.1F
C
T
*
5V
R
PU
5k
f
OUT
NB: ATTA (min),
f
OUT
= 0Hz
*
RT AND CT – SEE TABLE
SENSOR R
T
(R1 + P1) C
T
TMP35
TMP36
TMP37
11.8k + 500
16.2k + 500
18.2k + 1k
1.7nF
1.8nF
2.1nF
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
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:
f
OUT
V
=
− V
TMP
10 × RT× C
OFFSET
()
T
Figure 11. A Temperature-to-Frequency Converter
An offset trim network (f
circuit to set f
at 0 Hz when the temperature sensor’s mini-
OUT
OFFSET ) is included with this
OUT
mum 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.
TMP3x
V
S
R1*
V
OUT
GND
*SEE TEXT
FOR VALUES
P1*
20mA
ADJUST
R3*
R2*
P2*
4mA
ADJUST
7
3
2
D1
D1 : HP5082–2810
A1 : OP193
4
R4*
3V
6
REF193
1F
0.1F
R5
100k
4
R6
100k
2
100
R7
Figure 10. A Temperature to 4-to-20 mA Loop Transmitter
–12–
Q1
2N1711
I
L
V
LOOP
9V TO 18V
V
OUT
R
250
L
REV. B
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 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.
+V
S
750
V
0.1F
TMP3x
GND
OUT
LONG CABLE OR
HEAVY CAPACITIVE
LOADS
Figure 12. 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 T
= 150°C) to an
J
observed shift in that parameter at 25°C. For any semiconductor
device, the acceleration factor is expressed as:
F = exp
E
1
a
×
T1
k
1
−
T 2
where F = Calculated acceleration factor;
E
= Activation energy in eV = 0.7 eV;
a
k = Boltzmann’s constant = 8.63 × 10
T1 = Test temperature in Kelvin, T
–5
eV/K;
= 150°C = 423.15 K;
J
and
T2 = Desired operating temperature in Kelvin,
= 25°C = 298.15 K
T
J
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 T
= 25°C. As quoted in the data sheet, the
A
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
= 150°C. To determine what the observed shift would be at
T
J
T
= 25°C is a matter of applying the acceleration factor calculated
A
above to this result:
4
0 01 3 23 10 0 003 25
./ . . /@°××= ° °
C day m C day C
−
Thus, if any of the TMP3x devices were to be used at 25°C, 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.
REV. B
–13–
TMP35/TMP36/TMP37
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
3-Lead Plastic Package
(TO-92)
0.135
(3.43)
MIN
SEATING
PLANE
0.500
(12.70)
MIN
0.105 (2.66)
0.095 (2.42)
0.105 (2.66)
0.080 (2.42)
0.105 (2.66)
0.080 (2.42)
123
BOTTOM VIEW
0.205 (5.20)
0.175 (4.96)
0.210 (5.33)
0.170 (4.38)
0.050
(1.27)
MAX
0.019 (0.482)
0.016 (0.407)
SQUARE
0.055 (1.39)
0.045 (1.15)
0.165 (4.19)
0.125 (3.94)
0.1574 (4.00)
0.1497 (3.80)
0.0098 (0.25)
0.0040 (0.10)
0.0669 (1.70)
0.0590 (1.50)
0.0512 (1.30)
0.0354 (0.90)
0.0059 (0.15)
0.0019 (0.05)
SEATING
PLANE
PIN 1
8-Lead SOIC
0.1968 (5.00)
0.1890 (4.80)
8
5
0.2440 (6.20)
41
0.2284 (5.80)
PIN 1
0.0500
(1.27)
BSC
0.0688 (1.75)
0.0532 (1.35)
0.0192 (0.49)
0.0138 (0.35)
5-Lead Surface Mount
RT-5 (SOT-23 Type)
0.1181 (3.00)
0.1102 (2.80)
4 5
1 3
2
0.0374 (0.95) BSC
0.0748 (1.90)
BSC
0.0197 (0.50)
0.0138 (0.35)
(R-8)
0.0098 (0.25)
0.0075 (0.19)
0.1181 (3.00)
0.1024 (2.60)
0.0571 (1.45)
0.0374 (0.95)
SEATING
PLANE
0.0196 (0.50)
0.0099 (0.25)
8°
0°
0.0500 (1.27)
0.0160 (0.41)
10°
0°
x 45°
0.0079 (0.20)
0.0031 (0.08)
0.0217 (0.55)
0.0138 (0.35)
Revision History
Location Page
Data Sheet changed from REV. A to REV. B.
Edits to SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Addition of new Figure 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Deletion of WAFER TEST LIMITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
–14–
REV. B
–15–
C00337a–0–9/01(B)
–16–
PRINTED IN U.S.A.
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