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AD536AJQ データシート(PDF) 4 Page - Analog Devices |
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AD536AJQ データシート(HTML) 4 Page - Analog Devices |
4 / 8 page REV. B AD536A –4– The input and output signal ranges are a function of the supply voltages; these ranges are shown in Figure 14. The AD536A can also be used in an unbuffered voltage output mode by discon- necting the input to the buffer. The output then appears unbuf- fered across the 25 k Ω resistor. The buffer amplifier can then be used for other purposes. Further the AD536A can be used in a current output mode by disconnecting the 25 k Ω resistor from ground. The output current is available at Pin 8 (Pin 10 on the “H” package) with a nominal scale of 40 µA per volt rms input positive out. OPTIONAL EXTERNAL TRIMS FOR HIGH ACCURACY If it is desired to improve the accuracy of the AD536A, the external trims shown in Figure 2 can be added. R4 is used to trim the offset. Note that the offset trim circuit adds 365 Ω in series with the internal 25 k Ω resistor. This will cause a 1.5% increase in scale factor, which is trimmed out by using R1 as shown. Range of scale factor adjustment is ±1.5%. The trimming procedure is as follows: 1. Ground the input signal, VIN, and adjust R4 to give zero volts output from Pin 6. Alternatively, R4 can be adjusted to give the correct output with the lowest expected value of VIN. 2. Connect the desired full scale input level to VIN, either dc or a calibrated ac signal (1 kHz is the optimum frequency); then trim R1, to give the correct output from Pin 6, i.e., 1000 V dc input should give 1.000 V dc output. Of course, a ±1.000 V peak-to-peak sine wave should give a 0.707 V dc output. The remaining errors, as given in the specifications are due to the nonlinearity. The major advantage of external trimming is to optimize device performance for a reduced signal range; the AD536A is inter- nally trimmed for a 7 V rms full-scale range. Figure 2. Optional External Gain and Output Offset Trims SINGLE SUPPLY CONNECTION The applications in Figures l and 2 require the use of approxi- mately symmetrical dual supplies. The AD536A can also be used with only a single positive supply down to +5 volts, as shown in Figure 3. The major limitation of this connection is that only ac signals can be measured since the differential input stage must be biased off ground for proper operation. This biasing is done at Pin 10; thus it is critical that no extraneous signals be coupled into this point. Biasing can be accomplished by using a resistive divider between +VS and ground. The values of the resistors can be increased in the interest of lowered power consumption, since only 5 mA of current flows into Pin 10 (Pin 2 on the “H” package). AC input coupling requires only capacitor C2 as shown; a dc return is not necessary as it is provided internally. C2 is selected for the proper low frequency break point with the input resistance of 16.7 k Ω; for a cutoff at 10 Hz, C2 should be 1 µF. The signal ranges in this connection are slightly more restricted than in the dual supply connection. The input and output signal ranges are shown in Figure 14. The load resistor, RL, is necessary to provide output sink current. C2 Figure 3. Single Supply Connection CHOOSING THE AVERAGING TIME CONSTANT The AD536A will compute the rms of both ac and dc signals. If the input is a slowly-varying dc signal, the output of the AD536A will track the input exactly. At higher frequencies, the average output of the AD536A will approach the rms value of the input signal. The actual output of the AD536A will differ from the ideal output by a dc (or average) error and some amount of ripple, as demonstrated in Figure 4. Figure 4. Typical Output Waveform for Sinusoidal Input The dc error is dependent on the input signal frequency and the value of CAV. Figure 5 can be used to determine the minimum value of CAV which will yield a given percent dc error above a given frequency using the standard rms connection. The ac component of the output signal is the ripple. There are two ways to reduce the ripple. The first method involves using a large value of CAV. Since the ripple is inversely proportional to CAV, a tenfold increase in this capacitance will affect a tenfold reduction in ripple. When measuring waveforms with high crest |
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同様の説明 - AD536AJQ |
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