DRV8842: Microstepping for stepper motor

th133

Part Number: DRV8842
Other Parts Discussed in Thread: DRV8824, DRV8881EEVM

I am using DRV8842 to control movement in a stepper motor. The step angle in my stepper motor is 1.8 degrees. How do I use microstepping to rotate the stepper motor by 1 step angle only?

over 8 years ago

0 Rick Duncan over 8 years ago

TI__Guru** 114905 points

Hi th133,

Please refer to Table 2 in the DRV8824 datasheet for reference. One step angle is a 90 degree change in electrical angle.

You will need two DRV8842 to control the stepper motor. Each DRV8842 can control the current in one winding by using the PH/EN and I4:0 inputs to implement this table.

The I4:0 sets the amount of current while the PH sets the current direction.

0 th133 over 8 years ago in reply to Rick Duncan

Intellectual 265 points

Hello Rick,

Thank you for the suggestion. I had a query though. Its mentioned in Table 2 of DRV8824 datasheet that, during a 1/32 step mode, changing from 2 to 3, gives an increment from 3 to 6 in electric angle. So how I obtain an increment from say (3 to 4) or (3 to 5) ?

Thank you,

Regards,

0 Rick Duncan over 8 years ago in reply to th133

TI__Guru** 114905 points

Hi th133,

Each electrical angle corresponding to a percentage of current based on a sine function. So electrical angle 3 = 5% of full current, and electrical angle 6 = 10% of full current. If you want to change from 3 to 4, build your sine table to adjust the current to the desired percentage.

0 th133 over 8 years ago in reply to Rick Duncan

Intellectual 265 points

Hello Rick,

In DRV8842, for a 5% relative current, I'm giving I[0001], while for 10% relative current, I'm giving I[0002]. So how can I increament i[xxxx] for a relative current between 5% and 10%?

Thank you,
Regards,

0 Rick Duncan over 8 years ago in reply to th133

TI__Guru** 114905 points

Hi th133,

To achieve current levels not available using I4:0, set the I4:0 to 11111 (1000%) and change the AVREF and BVREF input voltage.

This can be controlled by a DAC or a PWM.

0 th133 over 8 years ago in reply to Rick Duncan

Intellectual 265 points

I'll look into it . Thank you for your suggestions Rick.

0 th133 over 8 years ago in reply to th133

Intellectual 265 points

Hello again Rick,

May I ask as to how we can rotate by the same 1.8 degree, but in a DC motor using DRV8842 ?

Thank you,

Regards,

0 Rick Duncan over 8 years ago in reply to th133

TI__Guru** 114905 points

Hi th133,

DC motors are not designed to move like steppers. If you want to rotate 1.8 degrees and hold, it is recommended to use a stepper motor.

0 th133 over 8 years ago in reply to Rick Duncan

Intellectual 265 points

Hello Rick,

DRV8842 has 32 levels of current regulation. So can we not keep relative current at 5% and move the DC motor by 3 degrees and then stop the motor?

0 Rick Duncan over 8 years ago in reply to th133

TI__Guru** 114905 points

Hi th133,

The DRV8842 has as many levels of current regulation as you desire.

This level of microstepping can be accomplished by setting the I4:0 pins to 11111 (100%) and changing the ref input. Typically a DAC is used to control the reference voltage.

An example of this type of code can be found in the DRV8881EEVM.

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DRV8842: Microstepping for stepper motor