Limit current of L6206 bridge driver
I think you may have selected the wrong part for what you are trying to do. Without any extra circuitry, the L6206 will only provide voltage-mode control. If you set the duty cycle to 100%, you will end up with 

$${12V \over 4.5\Omega} \approx 2.7A$$

in the active phase.

You can reduce that by reducing the duty cycle, but if you want to have something that will control current for you, an L6207 might be better suited: