Process for Tuning VREF for TMC2208SilentStepStick is as follows:
Connect the VCC (V logic) pin to 3.3V or 5V. Connect the GND pin to the MCU’s GND Power the driver from the power supply (usually between 9-24V) through the VM and GND pins, Do not connect motor yet. Measure voltage between VREF and GND then adjust R4 potentiometer to clockwise or anticlockwise according to current requirement. VREF for SILENTSTEPSTICK is in in between. (0 to 2.5V) ,2.5V = 100%=1.77A RMS ,1.25V=50%=0.88A RMS,0.50V=20%=0.35A RMS. After configuration of VREF connect motor and run it. Please refer datasheet for more details about VREF and current.