In the datasheet there's this formula:

ITripMAX =3D VREF / ( 8 =D7 RS)

So if my VREF max is 0.5v and the max current of the chip is 2A then if I
want full current out of the thing I put in a 0.0313 current sense.

Right?   My current sense R's are way bigger than that, probably because I
didn't want to start with a lot of smoke, so I top out well below the
capacity of the chip.

DougM

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
Josh Koffman
Sent: Friday, December 11, 2009 7:20 AM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Stepper Motor Driver

On Fri, Dec 11, 2009 at 12:58 AM, Doug Metzler <doug.metzler@gmail.com>
wrote:
> the cap goes from wiper to ground. =A0I'll send you the schematic.
>
> What value to trim the pot to? =A0Hmm, I think I set it at midpoint and
never
> mucked with it. =A0So I suppose I've got some headroom.

Hm....interesting. I always thought current was a bigger issue when
you were trying to half step so you needed a better handle on what you
put through the motor. What did you use to calculate out the sense
resistors? I suppose they could be picked then the trimmer tweaked to
provide the right current.

Josh
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