Datasheet TMP35, TMP36, TMP37 (Analog Devices) - 10

TMP35/TMP36/TMP37 Data Sheet BASIC TEMPERATURE SENSOR CONNECTIONS FAHRENHEIT THERMOMETERS
Figure 24 il ustrates the basic circuit configuration for the Although the TMP35/TMP36/TMP37 temperature sensors are TMP35/TMP36/TMP37 temperature sensors. The table in centigrade temperature sensors, a few components can be used Figure 24 shows the pin assignments of the temperature sensors to convert the output voltage and transfer characteristics to for the three package types. For the SOT-23, Pin 3 is labeled NC, directly read Fahrenheit temperatures. Figure 25 shows an as are Pin 2, Pin 3, Pin 6, and Pin 7 on the SOIC_N package. It example of a simple Fahrenheit thermometer using either the is recommended that no electrical connections be made to these TMP35 or the TMP37. Using the TMP35, this circuit can be pins. If the shutdown feature is not needed on the SOT-23 or on used to sense temperatures from 41°F to 257°F with an output the SOIC_N package, the SHUTDOWN pin should be transfer characteristic of 1 mV/°F; using the TMP37, this circuit connected to +VS. can be used to sense temperatures from 41°F to 212°F with an
2.7V < +V
output transfer characteristic of 2 mV/°F. This particular
S < 5.5V
approach does not lend itself to the TMP36 because of its
0.1µF
inherent 0.5 V output offset. The circuit is constructed with an AD589, a 1.23 V voltage reference, and four resistors whose
+VS
values for each sensor are shown in the table in Figure 25. The
SHUTDOWN TMP3x VOUT
scaling of the output resistance levels ensures minimum output
GND
loading on the temp-erature sensors. A generalized expression for the transfer equation of the circuit is given by  R1   R3 
PIN ASSIGNMENTS
V =  (TMP35)+  (AD589) OUT  R1+ R2   R3 + R4 
PACKAGE +V
   
S GND VOUT SHUTDOWN SOIC_N 8 4 1 5
where:
SOT-23 2 5 1 4
022
TO-92 1 3 2 NA
TMP35 is the output voltage of the TMP35 or the TMP37 at the 00337- Figure 24. Basic Temperature Sensor Circuit Configuration measurement temperature, TM. AD589 is the output voltage of the reference, that is, 1.23 V. Note the 0.1 µF bypass capacitor on the input. This capacitor should be a ceramic type, have very short leads (surface-mount The output voltage of this circuit is not referenced to the is preferable), and be located as close as possible in physical circuit’s common ground. If this output voltage were applied proximity to the temperature sensor supply pin. Because these directly to the input of an ADC, the ADC common ground temperature sensors operate on very little supply current and should be adjusted accordingly. may be exposed to very hostile electrical environments, it is
+VS
important to minimize the effects of radio frequency interference
0.1µF +V
(RFI) on these devices. The effect of RFI on these temperature
S
sensors specifical y and on analog ICs in general is manifested as
TMP35/ VOUT
abnormal dc shifts in the output voltage due to the rectification
TMP37 R1
of the high frequency ambient noise by the IC. When the
GND +
devices are operated in the presence of high frequency radiated or conducted noise, a large value tantalum capacitor (±2.2 µF)
R2
placed across the 0.1 µF ceramic capacitor may offer additional
VOUT
noise immunity.
AD589 R3 1.23V – R4 SENSOR TCVOUT R1 (kΩ) R2 (kΩ) R3 (kΩ) R4 (kΩ) TMP35 1mV/°F 45.3 10 10 374
023
TMP37 2mV/°F 45.3 10 10 182
00337- Figure 25. TMP35/TMP37 Fahrenheit Thermometers Rev. H | Page 10 of 19