Digital_potentiometer

Published:2009/7/25 5:25:00 Author:Jessie | From:SeekIC

Figure 9-31 shows a DAC0830 connected as a digital potentiometer (pot). The applied digital-input word multiplies the applied reference voltage. The resultant output voltage is the product of this multiplication, normalized to the resolution of the DAC. The op amp converts the DAC output current to a voltage through the 15-kΩ feedback resistor within the DAC. To preserve output linearity, the two current-output pins must be as close to 0 V as possible. Thus, the input-offset voltage of the op amp must be nulled. The amount of linearity-error degradation is about VOS + VREF When the digital pot is used to attenuate ac signals (in audio applications, for example), the DAC linearity over the full range of the applied reference voltage (even if it passes through zero) is good enough to distort a 10-V sine wave by only 0.004%. NATIONAL SEMICONDUCTOR, APPLICATION NOTE 271, 1994, P. 665.



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