TMP37FS View Datasheet(PDF) - Analog Devices
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TMP37FS Datasheet PDF : 16 Pages
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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 proxim-
ity 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 tanta-
lum capacitor (Ͼ2.2 µF) placed across the 0.1 µF ceramic may
offer additional noise immunity.
Fahrenheit Thermometers
Although the TMP3x temperature sensors are centigrade tem-
perature sensors, a few components can be used to convert the
output voltage and transfer characteristics to directly read Fahr-
enheit 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:
( ) ( ) VOUT
=
R1
R1+ R2
TMP 35
+
R3
R3 + R4
AD589
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
0.1F
VS
R1
TMP35/37 VOUT
GND
AD589
1.23V
R2
VOUT
R3
R4
PIN ASSIGNMENTS
SENSOR
TMP35
TMP37
TCVOUT R1 (k⍀) R2 (k⍀) R3 (k⍀) R4 (k⍀)
1mV/؇F 45.3
10
2mV/؇F 45.3
10
10
374
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.
0.1F
VS
VS
TMP36
VOUT
GND
R1
45.3k⍀
R2
10k⍀
VOUT @ 1mV/؇F – 58؇F
VOUT @ –40؇F = 18mV
VOUT @ +257؇F = 315mV
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 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 character-
istic 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
R3
TMP 36
−
R4
R3
VS
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 loca-
tions. 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; other-
wise, 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
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