TMP35/TMP36/TMP37

Rev. F | Page 10 of 20

BASIC TEMPERATURE SENSOR CONNECTIONS

Figure 24 illustrates the basic circuit configuration for the

TMP3x family of temperature sensors. The table in Figure 24

shows the pin assignments of the temperature sensors for the

three package types. For the SOT-23, Pin 3 is labeled NC, as are

Pin 2, Pin 3, Pin 6, and Pin 7 on the SOIC_N 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

on the SOIC_N package, the SHUTDOWN pin should be

0.1µF

GND

PACKAGE

GND

SOIC_N

8

4

1

5

SOT-23

2

5

1

4

TO-92

1

3

2

NA

PIN ASSIGNMENTS

SHUTDOWN

TMP3x

SHUTDOWN

Figure 24. Basic Temperature Sensor Circuit Configuration

Note the 0.1 μF bypass capacitor on the input. This capacitor

should be a ceramic type, have very short leads (surface-mount

is preferable), and be located as close as possible in physical

proximity to the temperature sensor supply pin. Because these

temperature sensors operate on very little supply current and

may be exposed to very hostile electrical environments, it is

important to minimize the effects of radio frequency interference

(RFI) on these devices. The effect of RFI on these temperature

sensors specifically and on 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. When 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 capacitor 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. Figure 25 shows an example of a

simple Fahrenheit thermometer using either the TMP35 or the

TMP37. Using the TMP35, 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 TMP37, this circuit can be

used to sense temperatures from 41°F to 212°F with an output

transfer characteristic of 2 mV/°F. This particular approach

does not lend itself 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 table in Figure 25. The scaling of the output

resistance levels ensures minimum output loading on the temp-

erature sensors. A generalized expression for the transfer

equation of the circuit is given by

()

()

AD589

R4

R3

R3

TMP35

R2

R1

R1

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+

+

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+

=

where:

TMP35 is the output voltage of the TMP35 or the TMP37 at the

AD589 is the output voltage of the reference, that is, 1.23 V.

The output voltage of this circuit is not referenced to the

circuit’s common ground. If this output voltage were applied

directly to the input of an ADC, the ADC common ground

should be adjusted accordingly.

SENSOR

TMP35

1mV/°F

45.3

10

10

374

TMP37

2mV/°F

45.3

10

10

182

R2 (kΩ)R3 (kΩ)R4 (kΩ)

TMP35/

TMP37

GND

R1

R2

R3

R4

AD589

1.23V

0.1µF

–

+

Figure 25. TMP35/TMP37 Fahrenheit Thermometers