Also as a note, all those do have Vref, where on the IC driver Vref is an input pin that takes in a voltage set by external components. Usually should be a potentiometer for the purpose to allow to vary the voltage. If there is no potentiometer, then probably there are some fixed resistors, to do the same thing e.g. create a voltage except this way the user cant change that voltage. Normally that should be adjustable for the purpose to be tweaked by user in a manner to provide appropriate current for the mechanics and not waste much more than that.
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