SLOSE70 December 2020 DRV8434S
Mixed decay begins as fast decay for an initial duration of the tOFF time, followed by slow decay for the remainder of tOFF time. In this mode, mixed decay occurs for both increasing and decreasing current steps.
This mode exhibits ripple larger than slow decay, but smaller than fast decay. On decreasing current steps, mixed decay settles to the new ITRIP level faster than slow decay.
When the winding current is held static for a long time (for example while no STEP input is present) or at very low step rates, slow decay may not properly regulate the current because back-EMF will be small or absent across the motor windings. In this case the motor current can rise rapidly and require an extremely long off-time to regulate the current. Increasing and decreasing current mixed decay mode allows the current to stay in regulation when no back-EMF is present across the motor windings.