DRV8711: Torque register sometimes does not change output level

SourceTwo

Part Number: DRV8711

Hello,

I have been using the DRV8711 with generally good results in a custom board. After each move, I need to maintain the current level for 2.5 seconds and then reduce it to about 33%. Usually this works as expected. However, sometimes the DRV8711 regulation level does not respond to the new Torque register value. I have verified the register is loaded with the desired values during motion, after stop and after the 2.5 second hold time.

Although the Torque register contents are verified, are there any conditions or circumstances that prevent the register contents from transferring to the internal circuitry? I have verified that the STEP input is at the LOW level when not stepping.

I look forward to hearing any ideas (or solutions) you may offer. Thank you!

Regards,

Dave

over 5 years ago

0 Wang5577 over 5 years ago

TI__Guru 56650 points

Dave,

Would you show me the good current waveform and bad current waveform? One example: if the motor winding inductance is small, the output current could shoot up over the regulation point before current sensing blanking time expired. With the winding current waveform, we may find the root cause.

0 SourceTwo over 5 years ago in reply to Wang5577

Expert 2355 points

Hello Wang,

Thank you for your response! Your question got me to exploring - I found that increasing the off time (pretty dramatically) helped the current decay to a more realistic value.

Regards,

Dave

0 Wang5577 over 5 years ago in reply to SourceTwo

TI__Guru 56650 points

Dave,

Yes. DRV8711 datasheet gives an application note talking about it: DRV8711 Decay Mode Setting Optimization (https://www.ti.com/lit/an/slva637/slva637.pdf ).

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DRV8711: Torque register sometimes does not change output level