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How to set the stepper motor current?

The best way to set the motor current is by measuring the voltage on the Vref pin (0...2.5V) and adjusting the voltage with the potentiometer. The maximum motor current is 1.77A RMS and is set via the 0.11Ohm sense resistors.

Irms = (Vref * 1.77A) / 2.5V = Vref * 0.71
Vref = (Irms * 2.5V) / 1.77A = Irms * 1.41 = Imax
Vref -> Voltage on Vref pin
Irms -> RMS (Root Mean Square) current per phase (Irms = Imax / 1.41)
Imax -> Maximum current per phase (Imax = Irms * 1.41)
Example: A voltage of 1.0V on Vref sets the motor current to 0.71A RMS.
Note: On some stepper motor drivers the maximum current (e.g. A4988) is set via Vref and on others the RMS current (e.g. TMC2100). The Trinamic drivers have an automatic thermal shutdown (at about 150°C) if the chip gets to hot.

Note: On some stepper motor drivers the maximum current (e.g. A4988) is set via Vref and on others the RMS current (e.g. TMC2100).