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ADC0804LCN bảng dữ liệu(PDF) 10 Page - Intersil Corporation |
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ADC0804LCN bảng dữ liệu(HTML) 10 Page - Intersil Corporation |
10 / 17 page 10 Such an adjusted reference voltage can accommodate a reduced span or dynamic voltage range of the analog input voltage. If the analog input voltage were to range from 0.5V to 3.5V, instead of 0V to 5V, the span would be 3V. With 0.5V applied to the VlN(-) pin to absorb the offset, the reference voltage can be made equal to 1/2 of the 3V span or 1.5V. The A/D now will encode the VlN(+) signal from 0.5V to 3.5V with the 0.5V input corresponding to zero and the 3.5V input corresponding to full scale. The full 8 bits of resolution are therefore applied over this reduced analog input voltage range. The requisite connections are shown in Figure 13. For expanded scale inputs, the circuits of Figures 14 and 15 can be used. Reference Accuracy Requirements The converter can be operated in a pseudo-ratiometric mode or an absolute mode. In ratiometric converter applications, the magnitude of the reference voltage is a factor in both the output of the source transducer and the output of the A/D converter and therefore cancels out in the final digital output code. In absolute conversion applicatIons, both the initial value and the temperature stability of the reference voltage are important accuracy factors in the operation of the A/D converter. For VREF/2 voltages of 2.5V nominal value, initial errors of ±10mV will cause conversion errors of ±1 LSB due to the gain of 2 of the VREF/2 input. In reduced span applications, the initial value and the stability of the VREF/2 input voltage become even more important. For example, if the span is reduced to 2.5V, the analog input LSB voltage value is correspondingly reduced from 20mV (5V span) to 10mV and 1 LSB at the VREF/2 input becomes 5mV. As can be seen, this reduces the allowed initial tolerance of the reference voltage and requires correspondingly less absolute change with temperature variations. Note that spans smaller than 2.5V place even tighter requirements on the initial accuracy and stability of the reference source. In general, the reference voltage will require an initial adjustment. Errors due to an improper value of reference voltage appear as full scale errors in the A/D transfer FIGURE 12. THE VREFERENCE DESIGN ON THE IC FIGURE 13. OFFSETTING THE ZERO OF THE ADC080X AND PERFORMING AN INPUT RANGE (SPAN) ADJUSTMENT V+ DGND VREF/2 AGND (VREF) R R DIGITAL CIRCUITS ANALOG CIRCUITS 9 810 20 DECODE 300 TO VREF/2 TO VIN(-) ZERO SHIFT VOLTAGE 0.1 µF 5V - + VREF (5V) FS ADJ. “SPAN”/2 ICL7611 FIGURE 14. HANDLING ±10V ANALOG INPUT RANGE FIGURE 15. HANDLING ±5V ANALOG INPUT RANGE VIN(-) 2R 5V 2R VIN ± 10V R VIN(+) (VREF) V+ 20 10 µF 6 7 + ADC0803- ADC0804 VIN(-) R 5V VIN ±5V R VIN(+) (VREF) V+ 20 10 µF 6 7 + ADC0803- ADC0804 ADC0803, ADC0804 |
Số phần tương tự - ADC0804LCN |
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Mô tả tương tự - ADC0804LCN |
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