Re: Allegro 3977

Hi,

That is not a problem. The purpose of a "sense" resistor is so that
the drive circuit has feedback or knowledge of what current is
flowing in the winding. The drive needs this info to adjust the
winding currents to the required values.

The "current sense" resistors are power resistors, but not like the
enourmous current limiting resistors needed in an R/L drive.

The chip is rated at 2.5A and the sense voltage is 0.5V, so using W =
I times V you get 1.25 Watts of dissipation. That's not a lot.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "ths992001" <thscarince@h...> wrote:
>
> Whoa, hold on! I'm looking at the datasheet that was posted last
> week and I see pins SENSE1 and SENSE2 that need power resistors to
> GND. They even state a max sense voltage of .5 volts... If they've
> changed that, great! Maybe I'm wrong.
>
> - Tom S.
>
> --- In CAD_CAM_EDM_DRO@y..., "y2patmat" <patmat2350@a...> wrote:
> > Hoo-yay, got my sample 3977's in... single chip, S/D in, 2.5a per
> > bipoler phase out, with on-board current limiting (no
> stinkin "power"
> > resistors).
> > I put a data sheet in the FILES section, which I'll try to
remember
> > to remove once Allegro gets it on their site.
> > Now, I just have to build my machine... details, details...
> > patmat