TB67S128FTG Microstepping Current Limit

Hi all,

I recently got TB67S128FTG Stepper Motor Driver Carrier and found the following instructions on the product page (Pololu - TB67S128FTG Stepper Motor Driver Carrier):

“For the microstep modes to function correctly, the current limit must be set low enough (see below) so that current limiting gets engaged. Otherwise, the intermediate current levels will not be correctly maintained, and the motor will skip microsteps”

On the same page, I didn’t find how current limit should be set low enough, in order to have correct microstep mode. Anyone can elaborate how current limit affect the correct operation of microstepping? From what I understood, increase of decrease current limit would simply scale the miscrosepping current proportionally…

In addition, what are the suggested settings for this stepper motor driver, for the purpose of getting microsteps as accurate as possible? My application is a DIY equatorial mount / star tracker which requires high pointing accuracy. Btw, I am using 1/32 microstepping mode on a 0.9deg stepper motor with 3.75x and 120x belt and worm gear reduction, respectively.

Thanks for any support from the community


The current limit should be set equal to or bellow your stepper motor’s rated current per phase (if this is not specified for your motor, you can calculate it by dividing the motor’s rated voltage by its coil resistance). The instructions for setting the current limit are on the product page under the “Current limiting” header. Setting the current limit properly is critical to prevent your driver or motor from being damaged (which is likely if the limit is too high) and to ensure that your motor has enough power to step reliably (which is likely if the limit is too low).

Your application sounds exciting! Unfortunately though, other than making sure your current limit is set properly, I do not have any specific suggestions for what settings you should use to maximize accuracy since that can probably vary between applications depending on the particular conditions. However, our carrier breaks out every control pin and output of the TB67S128FTG, so you can try out any of the features you are interested in to see how they affect performance in your system. I would be interested to hear your results!

- Patrick