DRV8834: Driving a small, low current stepper motor

Brian Markey

Part Number: DRV8834
Other Parts Discussed in Thread: DRV8880

I am attempting to drive a small stepper motor with the DRV8834. This motor has a 48 Ohm winding resistance and is intended to be operated at 4V. The peak current should be less than 100mA. We are micro stepping at 8x and see little motion for the micro steps then a big jump at the full step boundary. When I look at the current to the motor winding it goes to zero during each PWM cycle, regardless of step. If I could reduce fixed off time I assume the PWM might turn on again before the current goes to zero. Is there a more suitable driver for this small motor? I am looking at the DRV8880 and am intrigued by the Tourque DAC setting, is this a way to configure the IC to drive a smaller motor? Sorry but I do not know the winding inductance or the degrees per step for this motor. I am working from a rather weak stepper driven iris datasheet that I will attach.VP-9610(www) specification (optoskand151023 hunter170726).pdf

over 8 years ago

0 Brian Markey over 8 years ago

Prodigy 70 points

I want to correct my statement above. I looked at the current waveforms again and the winding current is going to zero each PWM cycle for current settings below about 40% of full scale. For relatively high current (above 40% of Ipk) the winding current stays positive for all PWM cycles in the step.
I really want to reduce the ripple current as a percentage of average current, perhaps slow decay all of the time?

0 Luis Riveros over 8 years ago in reply to Brian Markey

TI__Expert 4435 points

Hi Brian,
Yes you can use slow decay and give it a try. Also, what do you have for Rsense? What is your full scale current set to?

0 Brian Markey over 8 years ago in reply to Luis Riveros

Prodigy 70 points

Hello Luis;
I am running about 40mA full scale with an Rsense of 10 Ohms.
Thanks
Brian

0 Brian Markey over 8 years ago in reply to Brian Markey

Prodigy 70 points

Also, we are not missing steps at this current. We were missing steps at a slightly lower current. What bothers me is the fast decay in the current creating a sawtooth waveform that goes all the way to zero. I typically see a little PWM ripple riding on a significant DC current.

I will probably try slow decay next.

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DRV8834: Driving a small, low current stepper motor