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TMP35 Fiches technique(PDF) 9 Page - Analog Devices |
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TMP35 Fiches technique(HTML) 9 Page - Analog Devices |
9 / 20 page TMP35/TMP36/TMP37 Rev. F | Page 9 of 20 APPLICATIONS INFORMATION SHUTDOWN OPERATION All TMP3x devices include a shutdown capability, which reduces the power supply drain to less than 0.5 μA maximum. This feature, available only in the SOIC_N 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 +VS is connected. This allows the 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 off the output stage. During shutdown, the output of the temperature sensors becomes high impedance where the potential of the output pin is then determined by external circuitry. If the shutdown feature is not used, it is recommended that the SHUTDOWN pin be connected to +VS (Pin 8 on the SOIC_N; Pin 2 on the SOT-23). The shutdown response time of these temperature sensors is shown in Figure 14, Figure 15, and Figure 16. 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 and +125°C. Properly cemented or glued to the surface of the medium, these sensors are within 0.01°C of the surface temperature. Caution should be exercised, especially with T-3 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 temper- ature sensor and the hookup wires with a bead of thermally conductive epoxy. This ensures 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 non- conductive epoxy paints or dip or any one of the 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. Figure 23 illustrates a thermal model of the TMP3x temperature sensors, which is useful in under- standing these characteristics. TJ θJC TC θCA CCH CC PD TA Figure 23. Thermal Circuit Model In the T-3 package, the thermal resistance junction-to-case, θJC, is 120°C/W. The thermal resistance case-to-ambient, CA, is the difference between θJA and θJC, and is determined by the char- acteristics of the thermal connection. The power dissipation of the temperature sensor, PD, is the product of 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 ambient temperature of the medium is given by TJ = PD × (θJC + θCA) + TA Thus, the die temperature rise of a TMP35 SOT-23 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, CCH, and the case, CC. The thermal capacity of CC varies with the measurement medium because it includes anything in direct contact with the package. In all practical cases, the thermal capacity of CC is the limiting factor in the thermal response time of the sensor and can be represented by a single-pole RC time constant response. Figure 17 and Figure 19 show 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 SOIC package sensor mounted onto a 0.5" × 0.3" PCB is less than 50 sec in air, whereas in a stirred oil bath, the time constant is less than 3 sec. |
Numéro de pièce similaire - TMP35_10 |
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Description similaire - TMP35_10 |
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