DRV8308: Running at slow speed

Jacob,

This highly depends on the mode you are using (clock Frequency mode, clock PWM mode, internal speed mode). When using the internal speed mode there is a lower and upper bound to the control loop and this dominates the min/max electrical frequency. This combined with the number of poles of the motor will dictate it's speed capability.

From the datasheet Section (8.1.1): The built-in speed control loop is designed to work optimally with motor electrical speeds from about 50 Hz up to
6.7 kHz. For an 8-pole motor, this translates into about 500 RPM up to more than 100000 RPM. For motors with
higher pole counts, these speeds scale down; for lower pole counts, they scale up.

Regards,

-Adam

Yes, I saw that in the datasheet about the built-in speed control loop. But I also saw in the same section is says :
"When not using the internal speed loop (when controlling the motor using PWM input or register speed control),
the limits imposed by the speed loop do not apply. An external speed control implementation (using a
microcontroller, FPGA, or other logic) can essentially control the motor current directly."

And that's what the eval board is right, with the external MCU supplying the speed register or PWM input. So can I drive the motor that comes with the kit at 1 RPM with any combination of settings? I'm not specifying an application other than the eval kit. Can it be done?

Thanks

Jacob,

I think you would need an external clock to do this as the internal speed loop cannot get that low and I'm not sure the MCU can generate a clock this low either.

Regards,

-Adam

Ok, so the sense I'm getting is that this driver is not intended for slow speed, probably cannot run at slow speed with what's shipped in the dev kit, and it hasn't been tried over at TI.  Is that accurate?  If so that's fine, I'd just like to know so I can try to find another chip.  Can you recommend anything?  We liked this because we didn't have to worry about the commutation ourselves.

Thanks

Jacob