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AD680JR Datasheet(PDF) 6 Page - Analog Devices |
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AD680JR Datasheet(HTML) 6 Page - Analog Devices |
6 / 8 page AD680 REV. C –6– TEMPERATURE PERFORMANCE The AD680 is designed for reference applications where tem- perature performancc is important. Extensivc temperature test- ing and characterization ensures that the device’s performance is maintained over the specified temperature range. Some confusion exists in thc area of defining and specifying ref- erence voltage error over temperature. Historically, references have been characterized using a maximum deviation per degree centigrade, i.e., ppm/ °C. However, because of nonlinearities in temperature characteristics which originated in standard Zener references (such as “S” type characteristics), most manufactur- ers now use a maximum limit error band approach to specify devices. This technique involves the measurement of the output at three or more different temperatures to specify an output voltage error band. SLOPE = TC = V – V MAX MIN –6 (T – T ) x 2.5V x 10 MAX MIN 2.501 – 2.498 85 C – (–40 C) x 2.5V x 10 = –6 = 9.6ppm/ C 2.501 2.500 2.499 2.498 –50 –30 –10 0 20 40 60 80 100 TEMPERATURE – C Figure 9. Typical AD680AN/AP Temperature Drift Figure 9 shows a typical output voltage drift for the AD680AN/ AR and illustrates the test methodology. The box in Figure 9 is bounded on the sides by the operating temperature extremes, and on the top and bottom by the maximum and minimum out- put voltages measured over the operating temperature range. The maximum height of thc box for the appropriate tempera- ture range and device grade is shown in Table I. Duplication of these results requires a combination of high accuracy and stable temperature control in a test system. Evaluation of the AD680 will produce a curve similar to that in Figure 9, but output read- ings may vary depending upon the test equipment utilized. TEMPERATURE OUTPUT PIN The 8-pin packaged versions of the AD680 provide a tempera- ture output pin on Pin 3 of each device. The output of Pin 3 (TEMP) is a voltage that varies linearly with temperature. VTEMP at 25 °C is 596 mV, and the temperature coefficient is 2 mV/ °C. Figure 10 shows the output of this pin over temperature. The temperature pin has an output resistance of 12 k Ω and is capable of sinking or sourcing currents of up to 5 µA without disturbing the reference output, enabling the temp pin to be buffered by any of a number of inexpensive operational amplifi- ers that have bias currents below this value. 760 440 90 520 480 –40 –50 600 560 640 680 720 80 60 50 40 20 10 0 –10 –20 –30 30 70 TEMPERATURE – C Figure 10. Temp Pin Transfer Characteristic DIFFERENTIAL TEMPERATURE TRANSDUCER Figure 11 shows a differential temperature transducer that can be used to measure temperature changes in the AD680’s envi- ronment. This circuit operates from a +5 V supply. The tem- perature dependent voltage from the TEMP pin of the AD680 is amplified by a factor of 5 to provide wider full-scale range and more current sourcing capability. An exact gain of 5 can be achieved by adjusting the trim potentiometer until the output varies by 10 mV/ °C. To minimize resistance changes with tem- perature, resistors with low temperature coefficients, such as metal film resistors, should be used. 3 6 7 2 3 4 4 V IN TEMP GND AD680 +5V +5V R B R F R BP 100 Ω 1.69k Ω 1% 6.98k Ω 1% OP-90 2 0.1 µF = 10mV/ C OUT ∆V ∆T Figure 11. Differential Temperature Transducer LOW POWER, LOW VOLTAGE REFERENCE FOR DATA CONVERTERS The AD680 has a number of features that make it ideally suited for use with A/D and D/A converters. The low supply voltage required makes it possible to use the AD680 with today’s convertcrs that run on 5 V supplies without having to add a higher supply voltage for the reference. The low quiescent cur- rent (195 µA), combined with the completeness and accuracy of the AD680 make it ideal for low power applications such as handheld, battery operated meters. |
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