8824 output motor current abnormal

Hi ChungChing

Your abnormal one looks like under higher speed. It is normal to see the current waveform have distortion at higher speed. It will show that in the current going down section, the current can't decay to the target level till the current direction change.

This behavior is normal for all stepper driver. And auto-tune tech in DRV8880 will help to reduce this effect and achieve better waveform at higher speed. Please refer to the following video.

www.ti.com/.../support

If the motor running smoothly and still have enough torque margin, the distortion on current waveform will be no harm to the application. When speed goes down, the current waveform will back to normal again.

Best regards,

Hi Wilson,

I have try to down motor speed,but the distortion still exist,

Only if I increase Curent, the current wave form become smooth.

below figure is yesterday my setting with distortion current waveform.

I have to increase current to 3A, and the current distortion disappear.

This is different to " It is normal to see the current waveform have distortion at higher speed"

Now our application found motor noise problem

May this result in noise problem?

Thanks for your support

Hi ChungChing

Please use mixed or fast decay setting for microstepping. In EVM you can just open the decay pin jumper to get mixed decay.

If in slow decay, you will see the distortion like that. Slow decay is more often used for Full or Half stepping.

Best regards,

Hi Wilson,

We found that the decay mode setting is the rootcasue of noise problem,

If we set fast or mixed mode, the current waveform become more smooth for 32 microstep.

But here still some questions we want to know:

1. Why "Slow decay is more often used for Full or Half stepping"? Is there any theoretical basis? so we can't use slow mode for 32 microstep setting?

2. It seems that Mixed mode is less noise than fast mode, Is there any other method to down noise? ex. add capacity or?

3. What should we notice when changing fast(or mixed) mode to slow mode at standby?(it looks like that slow mode have more clear current waveform (noise smaller) than fast mode) 

 Thanks for your fully support!!

   Dear sir,

Any update?

Thanks a lot~

Hi ChungChing,

1. Why "Slow decay is more often used for Full or Half stepping"? Is there any theoretical basis? so we can't use slow mode for 32 microstep setting?

>In high level microstepping, in the current decreasing section (Please refer to Fig15 of DRV8880 datasheet www.ti.com/.../drv8880.pdf ), the current can't be decayed to the index requested level in time with slow decay for most stepper motors at mid to high speed range.

2. It seems that Mixed mode is less noise than fast mode, Is there any other method to down noise? ex. add capacity or?

> DRV8824 can't change the decay mode parameters in a detail way. So there is almost nothing to do with it. But DRV8846, DRV8711, DRV8880, DRV8818 are open to do further tuning of the decay mode which may help to reduce the noise (just get the current ripple down and shaping smoothly). Note auto-tune in DRV8880 just give you perfect decay parameters according to your motor automatically.


3. What should we notice when changing fast(or mixed) mode to slow mode at standby?(it looks like that slow mode have more clear current waveform (noise smaller) than fast mode)

> Yes. It is a good way to switch the mode to slow decay when the motor is in holding state. But must make sure that the current level is still meet with the setting level in slow decay. Because it is possible for some motor the current will lost regulation in slow decay if the current rising slew rate is too fast. The current decay amount in the whole slow decay section is not able to reduce the current jumping up in the Tblanking time section.

Best regards,

Dear sir,

Please help to show us the advantage and disadvantage of these three decay mode : slow,fast andmixed.
and the suggestion setting for different situation,

ex:
slow mode for Full or Half stepping.
and fast mode?
Mixed mode?
what's the different between fast and mixed mode?



Thanks for your fully support~