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AD22100KR-REEL7 データシート(PDF) 9 Page - Analog Devices |
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AD22100KR-REEL7 データシート(HTML) 9 Page - Analog Devices |
9 / 12 page AD22100 Rev. D | Page 9 of 12 Response of the AD22100 output to abrupt changes in ambient temperature can be modeled by a single time constant t expo- nential function. Figure 10 shows the typical response time plots for a few media of interest. 100 0 100 30 10 10 20 0 60 40 50 70 80 90 90 80 70 60 50 40 30 20 STILL AIR TIME (sec) ALUMINUM BLOCK MOVING AIR Figure 10. Response Time The time constant t is dependent on θJA and the thermal capaci- ties of the chip and the package. Table 6 lists the effective t (time to reach 63.2% of the final value) for a few different media. Copper printed circuit board connections were neglected in the analysis; however, they will sink or conduct heat directly through the AD22100’s solder plated copper leads. When faster response is required, a thermally conductive grease or glue between the AD22100 and the surface temperature being measured should be used. MICROPROCESSOR A/D INTERFACE ISSUES The AD22100 is especially well suited to providing a low cost temperature measurement capability for microprocessor/ microcontroller based systems. Many inexpensive 8-bit micro- processors now offer an onboard 8-bit ADC capability at a modest cost premium. Total cost of ownership then becomes a function of the voltage reference and analog signal conditioning necessary to mate the analog sensor with the microprocessor ADC. The AD22100 can provide an ideal low cost system by eliminating the need for a precision voltage reference and any additional active components. The ratiometric nature of the AD22100 allows the microprocessor to use the same power supply as its ADC reference. Variations of hundreds of mil- livolts in the supply voltage have little effect as both the AD22100 and the ADC use the supply as their reference. The nominal AD22100 signal range of 0.25 V to 4.75 V (−50°C to +150°C) makes good use of the input range of a 0 V to 5 V ADC. A single resistor and capacitor are recommended to pro- vide immunity to the high speed charge dump glitches seen at many microprocessor ADC inputs (see Figure 2). An 8-bit ADC with a reference of 5 V will have a least signifi- cant bit (LSB) size of 5 V/256 = 19.5 mV. This corresponds to a nominal resolution of about 0.87°C. USE WITH A PRECISION REFERENCE AS THE SUPPLY VOLTAGE While the ratiometric nature of the AD22100 allows for system operation without a precision voltage reference, it can still be used in such systems. Overall system requirements involving other sensors or signal inputs may dictate the need for a fixed precision ADC reference. The AD22100 can be converted to absolute voltage operation by using a precision reference as the supply voltage. For example, a 5.00 V reference can be used to power the AD22100 directly. Supply current will typically be 500 µA, which is usually within the output capability of the reference. Using a large number of AD22100s may require an additional op amp buffer, as would scaling down a 10.00 V ref- erence that might be found in instrumentation ADCs typically operating from ±15 V supplies. 1 The time constant t is defined as the time to reach 63.2% of the final temperature change. 2 1200 CFM. |
同様の部品番号 - AD22100KR-REEL7 |
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同様の説明 - AD22100KR-REEL7 |
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