Looking at it now I don't think the 2.2k on top of the 10k pot is right -
with that combination your Vref max goes way higher than 0.5v, so be
careful.

I'm going to review it on my board.

DougM

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
Josh Koffman
Sent: Saturday, December 12, 2009 10:02 AM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Stepper Motor Driver

On Fri, Dec 11, 2009 at 11:32 PM, Doug Metzler <doug.metzler@gmail.com>
wrote:
> 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? =A0 My current sense R's are way bigger than that, probably becaus=
e I
> didn't want to start with a lot of smoke, so I top out well below the
> capacity of the chip.

Hi Doug,

It wasn't the math that was tripping me up, I think it was that I
didn't know where to start, Vref or resistor. Seems to make sense to
me now, and I like the idea of putting in a pot on Vref so it can be
tweaked.

Thanks!

Josh
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