ADC0816_14 Datasheet, PDF (11/19 Pages) Texas Instruments – ADC0816/ADC0817 8-Bit μP Compatible A/D Converters with16-Channel Multiplexer

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ADC0816, ADC0817
SNAS527C – JUNE 1999 – REVISED MARCH 2013
Figure 9. Ratiometric Conversion System
The ADC0816 needs less than a milliamp of supply current so developing the supply from the reference is
readily accomplished. In Figure 11 a ground references system is shown which generates the supply from the
reference. The buffer shown can be an op amp of sufficient drive to supply the milliamp of supply current and the
desired bus drive, or if a capacitive bus is driven by the outputs a large capacitor will supply the transient supply
current as seen in Figure 12. The LM301 is overcompensated to insure stability when loaded by the 10 μF output
capacitor.
The top and bottom ladder voltages cannot exceed V_CCand ground, respectively, but they can be symmetrically
less than V_CC and greater than ground. The center of the ladder voltage should always be near the center of the
supply. The sensitivity of the converter can be increased, (i.e., size of the LSB steps decreased) by using a
symmetrical reference system. In Figure 13, a2.5V reference is symmetrically centered about V_CC/2 since the
same current flows in identical resistors. This system with a 2.5V reference allows the LSB to be half the size of
the LSB in a 5V reference system.
Figure 10. Ground Referenced Conversion System Using Trimmed Supply
Figure 11. Ground Referenced Conversion System with Reference Generating V_CC Supply
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