Don't know where to buy A3982 from Allegro MicroSystems, but anyway...

From
http://www.electronicstalk.com/news/alb/alb195.html

-----------------
If the change is to a lower current, then the decay mode is set to
mixed decay with 31.25% fast and 68.75% slow decay.
This patented current decay scheme results in reduced audible noise,
increased step accuracy and reduced power dissipation.
----------------

Mike

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