I have a TB6660 Stepper driver and I gave pulse from an Arduino board. According to the TB6660 datasheet, drier should out a sine wave that created by using give square wave from Arduino.

But, when I connect the 2 channel oscilloscope to A+ and A- separately, it outputs only inverted square wave. A+ and A-

I used several Microstep modes. But, same result(only change the frequency)

Please describe the reason for that.


1 Answer 1


You probably have not attached a load. The stepper driver aims for a specific current through the coil and will put out the full voltage as long as this current is not reached, then turn off.

The inductivity of the coil will then act as a low-pass filter on the current. A flyback diode protects the FETs.

It may help to think of the arrangement as a buck converter with the feedback voltage derived from a shunt resistor (i.e. controlling current), combined with an H-bridge (sharing the power FETs).

Note that the stepper driver will expect an inductive load. If you connect a resistive load, you will not get a sensible output either (expect a high frequency square wave).

The load will need a minimum inductivity to give the driver time to switch off after reaching the target current.

  • \$\begingroup\$ I have attached a stepper motor as the load. Motor is rotating correctly.But there is no sine shape wave. \$\endgroup\$
    – user_fs10
    Dec 5, 2018 at 11:05
  • 1
    \$\begingroup\$ The current is supposed to be a sine shape. The voltage is whatever will bring the current close to that shape, with the constraint that the driver's FET can only be turned on or off (to avoid wasting energy). Try adding a small resistor (10–100mΩ) in series, and measure the voltage across that, to get current. \$\endgroup\$ Dec 5, 2018 at 12:50
  • \$\begingroup\$ Yes.You are correct. the current wave form should be sine shape. TB6660 datasheet has current in their graphs. I already did as you told. I attached 0.25Ohms resistors in series. because I haven't a current prob for my oscilloscope. But result is same. I couldn't get any sine shape wave. \$\endgroup\$
    – user_fs10
    Dec 6, 2018 at 3:58

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