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ISO100 Datasheet(PDF) 10 Page - Burr-Brown (TI) |
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ISO100 Datasheet(HTML) 10 Page - Burr-Brown (TI) |
10 / 15 page 10 ISO100 Example 4. Given: Total error RTO from Examples 1 and 3 as 378mV worst case. Find: Percent error of +10V full scale output % Error = x 100% = x 100% = 3.78% NOISE ERRORS Noise errors in the unipolar mode are due primarily to the optical cavity. When the full 60kHz bandwidth is not needed, the output noise of the ISO100 can be limited by either a capacitor, C F, in the feedback loop or by a low-pass filter following the output. This is shown in Figure 4. Noise in the bipolar mode is due primarily to the reference current sources, and can be reduced by the low-pass filters shown in Figure 5. V ERR TOTAL V FS OPTIONAL ADJUSTMENTS There are two major sources of offset error: offset volt- age and offset current. VOSI and VOSO of the input and output amplifiers can be adjusted independently using external potentiometers. An example is shown in Figure 17. Note that VOSO (500µV, max) appears directly at the output, but VOSI appears at the output multiplied by gain (RF/RIN). In general, VOS is small compared to the effect of IOS (see Example 1). To adjust for IOS use a circuit which intentionally unbalances the offset in one direction and then allows for adjustment back to zero. Figure 6 shows how to adjust unipolar errors at zero input. The unipolar amplifier can be used down to zero input if it is made to be “slightly bipolar.” By sampling the reference current with R 5 and R6, the minimum current required to keep the input stage in the linear region of operation can be established. R 7 and R8 are adjusted to cancel the offset created in the input stage. This brings the output to zero, when the input is zero. Although the amplifier can now operate down to zero input voltage, it has only a small portion of the current drain and noise that the true bipolar configuration would have. Adjusting the bipolar errors is illustrated in Figure 7. Each of the errors are adjusted in turn. With VIN = “open,”, IOS is trimmed by adjusting R 10 to make the output zero. RG is then adjusted to trim the gain error. The effects of offset voltage are removed by adjusting R 14. FIGURE 4. Two Circuit Techniques for Reducing Noise in the Unipolar Mode. FIGURE 5. Circuit Techniques for Reducing Noise from the Current Sources in the Bipolar Mode. FIGURE 6. Adjusting the Unipolar Amplifier Errors at Zero Input. 378mV 10V R I IN R F C C F 7 9 15 17 ISO100 3 18 f O = 1 2 πRC f O = 1 2 πR FCF I IN 7 9 15 17 ISO100 3 18 100k Ω 16 1µF 1M Ω R F 8 100k Ω 1µF V OUT R F 1M Ω V OUT Optional Unipolar I OS Adjust. I C2 R 6 84k Ω +In –In 18 λ R 7 10M Ω R 8 200k Ω Pot I REF 2 I REF 1 I C1 I IN R 5 10M Ω V OUT I IN I C2 (MAX) I C2 (MIN) Shift due to R 7 and R8. Shift due to R 5 and R6. ISO100 |
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Similar Description - ISO100 |
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