DRV8305: Dwell States

Hi Rohit,

The dwell state timing will primarily depend on the rotation speed, motor current, and the inductance/resistance of the phase windings in your motor. Dwell states work to reduce the sudden current changes that happen when the commutation pattern switches from one phase to the next. When the new current begins flowing through the previously inactive motor phase, it's like applying a step function to a series RL circuit: the inductor will oppose the new current flow. The dwell state allows current to start flowing into the new phase before the previous phase is turned off, smoothing the transition.

There's really not a great way to calculate the amount of dwell time to use. A good minimum bound would be to calculate or measure the turn-on time of your external FET, since enabling the dwell state for less time than it takes the FET to turn on won't help smooth the current flow. I'd suggest starting there, and increasing until you reach your desired acoustic performance. Do keep in mind, however, that dwell states to sacrifice some of the torque capability of the motor, so you will want to find a balance between performance and noise.

Thanks,
Garrett