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TMP37FT9-REEL Datasheet(PDF) 10 Page - Analog Devices |
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TMP37FT9-REEL Datasheet(HTML) 10 Page - Analog Devices |
10 / 20 page 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 connected to +VS. 2.7V < +VS < 5.5V VOUT 0.1µF +VS GND PACKAGE +VS GND VOUT 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 VOUT ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + + ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + = where: TMP35 is the output voltage of the TMP35 or the TMP37 at the measurement temperature, TM. 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 TCVOUT R1 (kΩ) 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 VOUT +VS VOUT +VS – + Figure 25. TMP35/TMP37 Fahrenheit Thermometers |
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