AN3525| Application Note
Maxim/Dallas > App Notes > DIGITAL POTENTIOMETERS Keywords: Potentiometer, digital pot, small step, resistor, variable, pseudo-log, transfer function, random, custom, Calculator, app note 3525
May 17, 2005
APPLICATION NOTE 3525
Resistor Calculator for the DS3906
The DS3906 contains three variable resistors that have a pseudolog response. External resistors can be used in parallel with the DS3906's resistors to achieve a linear response having small step sizes. This application note, along with the associated spreadsheet, demonstrates the ability to achieve a variable resistance with an effective linear response when used in parallel with external resistors. The spreadsheet also allows users to experiment with different values of external resistors to suit their particular application. The supplemental spreadsheet for this application note was developed in Microsoft Excel. Users can download the file, which contains two worksheets. The first worksheet, "WithoutExtR," contains the nominal values of the internal variable resistors for each of the programmed steps. This is simply a soft copy of the table in the DS3906 data sheet. The worksheet also calculates values of these resistors after considering the maximum variation (due to process changes) that the resistances
can have from the nominal values. A plot of the nominal resistance response without any external resistors is shown in Figure 1. Since R0 and R1 have the same response with respect to the resistor settings, only one graph is provided for both (R0,1).
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