Re: Allegro 3977SED questions

Michael,

Yes a capacitor across the sense resistor is needed to prevent noise
from false tripping the current sense comparator. Allegro recommends
a 0.1 uF ceramic capacitor. Bypass capacitors are also needed in
several other locations.

Allegro has an application note and a "frequently asked questions"
page for the A3977 chip. See:

http://www.allegromicro.com/techpub2/stp/stp01-2.pdf

http://www.allegromicro.com/faq/3977faq.htm#Q1

Regards,
Steve Stallings
www.PMDX.com


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "lomcevaktumble"
<lomcevaktumble@y...> wrote:

>
> Steve,
> Thanks so far for all your excellent help. I checked out your
> website and its clear you have a good understanding of the 3977 and
> CNC. I was very impressed!
>
> I am getting close to understanding all that I need to try and get
> this chip up and running - I'm just trying to make a simple setup
> with the minimum amount of parts that Allegro recommends.
>
> So you're recommending a .125 sense resistor...but I also notice in
> the diagram there is a capacitor. I'm assuming this is to help
> cancel out noise in the ciruit. Do I need a 0.1 uF or greater on
> this as well...or is it some other value??
>
> I feel like I should try and draw up what I plan on using where and
> seeing if you think it will work that way.
>
> Thanks again for all the help from everybody! I'm learning this
> slowly but surely!
>
> Michael
>