Allegro’s technical support is almost nonexistent…
I’m using a Pololu A4988 driver to run a small stepper motor using a 30 V supply. The stepper is rated for only 300 mA winding current, and I would like to use even less at times. Starting with a target of 1.4 * 300 mA, I set Vref to 228 mV with the little pot, then connected my motor (with power off). The motor steps fine (full steps) and has a strong holding torque, but the idling winding current is almost 600 mA peak, 530 mA average (measured with a DC current probe and a scope). When I reduce Vref, even to zero, the winding current barely goes lower than this.
The duty cycle on my windings is about 7.5%, and goes only slightly lower when I reduce Vref below 228 mV. I don’t see a minimum duty spec’d in the Allegro data sheet anywhere.
Does anyone know if 7.5% is about the minimum duty, or why I can’t reduce my winding current below 600 mA peak? Thanks for any help!