Ok, so I've made some changes to the circuit and a correction for my stepper.



First thing I did was to separate the phases to use two sensing resistors. My intention is to get a 40KHz chopping frequency to get it out of the audible range, and to get rid of the chopping code in my firmware.
Note: The values shown on the schematic are not for 40KHz, I can tweak that later.

Using the formula from the data sheet to calculate the needed resistor and capacitor for the R/C network, then using what I had available, yields around 30KHz.

I then set my V_REF = slightly below 1 volt to be able to get >3 Amps per phase, or a total of below 6 Amps through Fuse₁

When the circuit is powered up, I get a whopping .7 Amps total or 350 mA/phase. Now if I increase V_REF to 1.6V, I get a total current of about 1.5 Amps any farther than this and I get alot of noise coming from the motor at stand still and some funky distortion on the scope, then the current skyrockets to around 10 amps.

The upper trace in the following pictures is the sync pulse and the lower trace is V_Sense
BEWARE: These images are 1 to 2 megs each.


First signal is 5V/div, second is 1V/div @ 10uS/div
Scope1.jpg


This image is x5 magnification of above
Scope2.jpg

The following 3 pictures show the distortion that begins to occur as V_REF is increased.
Scope3.jpg
Scope4.jpg
Scope5.jpg


One of the application notes tells that noise can fool the comparator and the solution is to increase the sync pulse on-time to mask this noise, but when I do that I get an un-controllable high current, decreasing V_REF has no effect.

Any ideas?

Jon