I have written a question about this but I found new information in this video and I want to go more to the point.

My motor "rated current" is 1.4V. I assume that this is the maximum current


The guy explains in the video how to calculate the Vref and the X_CURRENT value of Marlin

RMS current = Max current / 1.41 = 1.3 / 1.41 = 0.92
Vref = (RMS Current x 2.5) / 1.77 = 1.3 V
90% Vref = 1.17 V       // to avoid maximum power in the motor
X_CURRENT = 1170 mA     // magic, I don't know why the guy of Teaching Tech does this convertion

Actually, I have read just now that one person says in a comment of the video:

[...] the numbers are wrong. When populating the current values in Marlin, it's asking for the RMS value in mA, not VREF. If we take the given values and take 90% of what's calculated, we'd end up with [...]

So the new calculation would be:

X_CURRENT = 90% RMS current = 0.92 * 0.90 = 0.828 A = 828 mA

I have also read in the TMC2130 datasheet:

Integrated power MOSFETs handle motor currents up to 1.2A RMS (QFN package) / 1.4A RMS (TQFP) or 2.5A short time peak current per coil.


  • Is he right? Why is he converting 1.17 V => 1170 mA directly?
  • The rated current shown in the motor datasheet is the same as the maximum current?
  • As 1.170 A < 1.2 A RMS or 0.828 A < 1.2 A RMS, the driver will not shut off, right?
  • Are my calculations right?

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