DRV8825: Output not available correctly

Poornalatha Arulselvan

Part Number: DRV8825

Sir,

We are designing a Stepper Motor Drive circuit using DRV8825.

Schematics for the same is attached for your reference.

The observation is, AOUT is not switching properly. Steps is not seen in the output. It is switching to 28V in the first index itself. Index is switching correctly. But output is switching between 28V & Ground.

Oscilloscope waveforms captured are attached for your reference.

CH1 : AOUT -- Full step Configuration

CH2 : STEP Input

CH1 : AOUT -- 8 micro step Configuration

CH2 : STEP Input

CH1 : BOUT - Full Step Configuration

CH2 : STEP Input

Schematics:

Regards,

KPL

over 3 years ago

0 Wang5577 over 3 years ago

TI__Guru 56650 points

Hello KPL,

"Index is switching correctly. But output is switching between 28V & Ground."

DRV8825 tries to regulate the winding current following the indexer table. Would you check the winding current to see if the winding current reaches the setting point or not? If the winding current is below the regulation point, the AOUT could be fully on.

0 Poornalatha Arulselvan over 3 years ago in reply to Wang5577

Prodigy 105 points

Sir,

Currently, AOUT and BOUT lines are open-ended. We have not connected any load to it.

Should I connect some Load Resistor /Inductor to simulate the Stepper motor?

Further, one more observation is BOUT is not behaving the same as AOUT. What could be the reason?

Regards,

KPL

0 Wang5577 over 3 years ago in reply to Poornalatha Arulselvan

TI__Guru 56650 points

KPL,

Please add a few mH inductor on the output. And then, check the output. let us have an output, and then, check AOUT and BOUT difference.

0 Poornalatha Arulselvan over 3 years ago in reply to Wang5577

Prodigy 105 points

Sir,

We connected 13mH across AOUT+ and AOUT-, the observation is as shown below.

CH1 : AOUT for HALF STEP

CH2 : STEP

It is observed the STEP Voltage dropping from 5V to 0.5V i.e it is getting loaded.

CHI: BOUT for HALF STEP

CH2: STEP

Regards,

KPL

0 Wang5577 over 3 years ago in reply to Poornalatha Arulselvan

TI__Guru 56650 points

KPL,

STEP pin is a high impedance input pin. Please measure the STEP pin impedance, if STEP pin is not damaged (low resistance to ground), please check the MCU's STEP pin control current capability.

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DRV8825: Output not available correctly