AD5161: Error in equation 4 / effect of wiper resistance, VW

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Accepted Answer

Question I am wondering how the wiper resistance influences the output voltage of a 
 digital potentiometer in voltage divider. In the AD5161 datasheet, there is 
 equation (4) on page 16 where Vw depends on Rwiper. Is this equation correct 
 (except the Raw replaced by 256)? Answer I’ll say that the correct equation should looks like:
 Vw(D)= Va∙Rwb(D)/Rab + Vb∙Rwa(D)/Rab
 Where Rwb(D) and Rwa(D) is the resistance between w and b/a terminals at any 
 specific code.
 
 There is an article that explain how is the internal digiPOT architecture,
 http://www.analog.com/library/analogDialogue/archives/45-08/digipot.html
 
 The wiper resistance in a digiPOT is the resistance due to the internal 
 switches.
 As there are always connected switches in the main signal path, the wiper 
 resistance effect should be add.

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AD5161: FAQ

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