DRV8711 Rate for changing the stepper mode

Hi Ralf,

There are two limits to be aware of when running the motor. First is the SPI frequency, which is 4MHz. Second is the motor limits. At higher levels of microstepping, the desired current may not be reached if stepping too quickly.

If you are changing the microstep mode while the motor is running, you should change the mode at a full step boundary. This will require keeping track of the number of steps issued.

Hallo Rick,

thats what I've read out of the datasheet, thank you.

One more question about your second sentence.

Apart from the issues of smooth motor running, is ist possible to change the stepping mode while motor is running,

or will this cause internal errors in the DRV8711?

For our application it could be nessecary to change the mode from 1/256 to 1/128 or from 1/128 to 1/164 while motor is running.

For higher stepping modes the change at a full step boundary is acceptable.

Hi Ralf,

Changing step mode while the motor is running does not cause an internal error in the DRV8711.

One more question about the DRV8711:

If we change the Mode e.g. from 1/8 to 1/4 step mode, normally we have to change the input frequency in time?

Corrrect?

But how to do this, because the mode we have to change with a SPI command, but the frequency with

hardware connection at STEP/AIN1 input.

There will apear a short delay for example 1-5 µseconds between this two actions.

Could cause a problem?

br Ralf

Hi Ralf,

Correct. If you change the mode from 1/8 to 1/4, you would normally half the frequency.

Minimizing the delay between the two actions is more of a mcu/firmware question. Since you are using the hardware STEP input, there could be a slight delay between changing the microstep mode and changing the STEP frequency.

Ideally you should change the microstep mode immediately after issuing the step command (may need an interrupt service routine), and if possible change the PWM input clock divider after that.