Book Analog Interfacing to Embedded Microprocessors
times a design calls for a variable resistance. Typical examples would be a
volume or tone control in a stereo, or gain control in an opamp circuit. In
these cases, a digital potentiometer is often the ideal solution. Like a DAC, a
digital potentiometer takes a digital word from a microprocessor, but it con-
verts it to a resistance instead of a voltage.
156 Analog Interfacing to Embedded Microprocessors
Figure 6.16
Video levels.
The Analog Devices AD5220 is a typical digital potentiometer (Figure
6.17). It comes in an 8-pin package, either DIP or surface mount, and in resis-
tance ranges of 10K, 50K, and 100K. It can operate at voltages from 3.3v to
5v. The AD5220 simulates a 3-terminal potentiometer with two terminals (A
and B) and a wiper (W). An internal 7-bit counter is decoded to determine
one of 128 positions for the wiper.
The AD5220 inputs consist of a clock (CLK), a chip select signal (-CS),
and an up/down control pin (U/D)
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