MCT8316Z: Overcome friction/motor lock condition?

Hi Nivant,

Thanks for your question on the Motor Drives E2E Forum. 

I will aim to provide an answer on this by the end of the week!

Best,

Robert

Hi Nivant,

Can you try spinning the motor without the load? If the motor can spin without load, that may give some indication that your schematic and layout is correct. If the motor cannot spin without the load then it might be a schematic or tuning issue with the motor. 

Best,

Robert

The motor spins while not loaded

Hi Nivant,

Can you confirm if you are using the SPI or hardware variant? 

Another thing to consider is how are you configuring the advance angle, slew, and mode pins. On the SPI variant, these are three configurable settings that can be tuned to increase motor performance. If not configured correctly, there may be issues.

If you can, please try to test out this motor configuration with the Evaluation Module (MCT8316ZEVM) found on the MCT8316Z product page.

Best,

Robert

I am using the hardware variant. I have, however, included connections on the PCB so that I can configure these pins. Currently I have them set to the defaults with advance set to 30 degrees. Can you maybe suggest what other settings make sense or what I might be able to expect by changing the slew rate or advance angle? I'm having trouble understanding how these pins will affect the motor performance? I will try to evaluate with the EVM module.

Hi Nivant,

You may want to configure the Advance Angle Settings according to the datasheet and its 7 different available levels based on an external resistor:

To learn more about lead angle adjustment, please refer to this TI Precision Labs video: https://training.ti.com/lead-angle-adjustment?context=1139747-1138777-1139742-1148348

Best,

Robert

Hi Nivant,

The default slew rate is also on the lower end. If you set the slew rate to 200 V/us you may see improvements.

Best,

Robert

Hi,

Nivant Desai said:

This assembly applies some friction for the motor to overcome. I am a bit confused as to how to interpret the problem I am having. Basically, I am giving the motor 100% duty cycle to try to get it to overcome the friction and just spin as much as it can. However, the motor simply produces a buzzing sound and the nFault condition is pulled low. I think that it is entering a motor lock condition because all the other conditions seem not to be violated. The current draw is only about 0.7A (well below the Ilimit threshold). 

When did you measure the 0.7A current? As soon as the motor got 100% duty cycle, there must be a huge current as the motor was stalled, then the driver shut down due to OC protection. You don't want to give 100% PWM to a stalled motor, as it gives a big jerk and trip the current protection. 

Is your application a position control or a velocity control? I would ramp up the pwm duty slowly until the load is moving, then I use that PWM as the threshold at the start output value and increase the value as needed.

Btw, did you calculate the motor current at 100% duty pwm at stall condition (zero motor speed)? It is very large for low resistance motor windings. Says for 1 ohm motor resistance phase to phase, at VM=24v, then at 100% pwm duty, the motor current is close to 24A before the motor can spin.

Brian