I understood the function of the drivers as follows. They are switch mode constant current converters. First they switch supply voltage directly to the motor. Since the windings are inductors the current rises slowly. Once the current has reached the configured current the supply voltage will be switched off. As a result the current decreases until a hysteresis value has reached. If reached the drivers switches voltage back on, again. If you increase your supply voltage the rise and fall time (slew rate) will increase, too. As a result your driver has to switch more often to maintain a regulated current window. Your frequency is rising with higher voltage, lower hysteresis and lower "waiting/off" times.
In my case I have motors with 900mA and a voltage at this operating point of 4V. 12V are enough to fry them anyways. 26V would make it faster :D
In my case I have motors with 900mA and a voltage at this operating point of 4V. 12V are enough to fry them anyways. 26V would make it faster :D