AD5272_wiper resistance

Document created by analog-archivist Employee on Feb 23, 2016Last modified by analog-archivist Employee on Feb 23, 2016
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As specified in the section of SPECIFICATIONS in its datasheet, the wiper
resistance when code is zero scale should be 35ohm (typical) and 70ohm (max). 
Refer to figure1 in the attachment
However, it is said in page 23 of the datasheet that in the zero-scale
condition, a finite total wiper resistance of 120 Ω is present. It seems to be
a contradiction?

 

If you see figure 46, you can see that there are a few switches in the signal
path.
Traditionally, the wiper resistance is mainly the last switch  resistance.
That’s why the resistance at zero scale is different than specified.
The other two switches in the path are already computed for the final LSB
value, so the only exception is zero scale code, where the switches cannot be
hidden.
You can find more info in this article,   
http://www.analog.com/library/analogDialogue/archives/45-08/digipot.html

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