DRV8424: stepper motor is too hot

Cherry Zhou

Part Number: DRV8424

Hi team,

Here's an issue from the customer may need your help:

Use the chip to drive a two-phase stepper motor with a current rating of 1.5A and a chip set current of 1.5A.

When the motor is running to a standstill, after a period of time, the motor is hot enough to heat up to 80℃. The current on the coil is approximately 0.75 a, and the static torque of the motor is also large.

The customer wants to reduce this quiescent current to 25% of the rated current. Is there any way to achieve it?

Could you help check this case? Thanks.

Best Regards,

Cherry

over 2 years ago

0 Jacob Thompson over 2 years ago

TI__Mastermind 23140 points

Hey Cherry,

They would just change the VREF input voltage to an appropriate amount to limit the current to 25% when stopped. This is detailed in 7.3.4 of the datasheet. The equation for calculating the regulation current is in 7.3.5 Current Regulation

Regards,

Jacob Thompson

0 Cherry Zhou over 2 years ago in reply to Jacob Thompson

TI__Mastermind 22235 points

Hi Jacob,

Thanks for your support. Here's a new question:

Is the output current of the chip half the rated current without the number of pulses? Since form the actual measurements, it is found that there is such a pattern.

Thanks and regards,

Cherry

0 Jacob Thompson over 2 years ago in reply to Cherry Zhou

TI__Mastermind 23140 points

Hey Cherry,

Is the measured 0.75A coil current measuring just one coil, so the total of the two coils is 1.5A?

There also might be confusion between Peak (full-scale) and RMS current, this training explains the difference: Video / PDF / Another page. This would apply if the customer is using microstepping.

You can see information about the DRV8424 peak vs RMS current rating in Table 7-2. Current Ratings

Regards,

Jacob Thompson

0 Cherry Zhou over 2 years ago in reply to Jacob Thompson

TI__Mastermind 22235 points

Hi Jacob,

Customer is setting a peak current of 1.5A.

During the actual motor motion, the current of one phase of the acquisition motor is sinusoidal with a peak value of 1.5A. When the motor is stopped, the current waveform changes to 0.75A DC.

Thanks and regards,

Cherry

0 Shinya Morita over 2 years ago in reply to Cherry Zhou

TI__Mastermind 36435 points

Hi,

Our expert is reviewing your feedback. Will reply to you within 24hours.

regards

Shinya Morita

0 Jacob Thompson over 2 years ago in reply to Cherry Zhou

TI__Mastermind 23140 points

Hey Cherry,

Could you post an oscilloscope shot of this happening? Does the current immediately drop in half when the motor stops, or does it slowly decay over a few seconds? And are they changing any other pins when motor stopped, or just not sending any more STEP signals?

I am not sure if what you describe is normal or not, I am going to ask my team and see what they think.

Regards,

Jacob

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DRV8424: stepper motor is too hot