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AD22100KR 데이터시트(PDF) 7 Page - Analog Devices |
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AD22100KR 데이터시트(HTML) 7 Page - Analog Devices |
7 / 12 page AD22100 Rev. D | Page 7 of 12 THEORY OF OPERATION The AD22100 is a ratiometric temperature sensor IC whose output voltage is proportional to its power supply voltage. The heart of the sensor is a proprietary temperature-dependent resistor, similar to an RTD, which is built into the IC. Figure 7 shows a functional block diagram of the AD22100. V+ VOUT RT Figure 7. Simplified Block Diagram The temperature-dependent resistor, labeled RT, exhibits a change in resistance that is nearly linearly proportional to temperature. This resistor is excited with a current source that is proportional to the power supply voltage. The resulting voltage across RT is therefore both supply voltage proportional and line- arly varying with temperature. The remainder of the AD22100 consists of an op amp signal conditioning block that takes the voltage across RT and applies the proper gain and offset to achieve the following output voltage function: VOUT = (V+/5 V) × (1.375 V + 22.5 mV/°C × TA) ABSOLUTE ACCURACY AND NONLINEARITY SPECIFICATIONS Figure 8 graphically depicts the guaranteed limits of accuracy for the AD22100 and shows the performance of a typical part. As the output is very linear, the major sources of error are off- set, for instance error at room temperature, span error, and de- viation from the theoretical 22.5 mV/°C. Demanding applica- tions can achieve improved performance by calibrating these offset and gain errors so that only the residual nonlinearity re- mains as a significant source of error. TEMPERATURE ( °C) 4 –4 150 –2 –3 –50 0 –1 1 2 3 100 50 0 TYPICAL ERROR MAXIMUM ERROR OVER TEMPERATURE MAXIMUM ERROR OVER TEMPERATURE Figure 8. Typical AD22100 Performance OUTPUT STAGE CONSIDERATIONS As previously stated, the AD22100 is a voltage output device. A basic understanding of the nature of its output stage is useful for proper application. Note that at the nominal supply voltage of 5.0 V, the output voltage extends from 0.25 V at –50°C to +4.75 V at +150°C. Furthermore, the AD22100 output pin is capable of withstanding an indefinite short circuit to either ground or the power supply. These characteristics are provided by the out- put stage structure shown in Figure 9. V+ VOUT Figure 9. Output Stage Structure The active portion of the output stage is a PNP transistor, with its emitter connected to the V+ supply and its collector connected to the output node. This PNP transistor sources the required amount of output current. A limited pull-down capa- bility is provided by a fixed current sink of about −80 µA, with the term fixed referring to a current sink that is fairly insensitive to either supply voltage or output loading conditions. The cur- rent sink capability is a function of temperature, increasing its pull-down capability at lower temperatures. |
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