DRV8301: Overcurrent protection and VDS register settings

Richard Bovenkerk

Part Number: DRV8301

Dear Engineers,

I am currenly busy with a redesign of a existing motor controller. The original design was based on a NXP/DRV8301 evaluation kit.
So most settings are same as this kit.

For my redesign I used another NFET: IPB083N10N3. Original we used NFET AOB290L.

In the end product, at first it seemed to work, but sometimes the motor stopped spinning. After looking into the issue; changing the VDS from default setting 0,06V to 20V seemed to solve the issue.
But are we really solving the issue? Since the connected motor doesn't draw that much current?

I try to get better understanding of this issue. Is it possible that the fet is not yet fully switched on? Or is it possible that a wrong dead time setting results in too high current flow?

Any advice how to test this further? Looking forward to your ideas.

Regards,

Richard

over 5 years ago

0 Richard Bovenkerk over 5 years ago

Prodigy 70 points

//edit
changing the VDS from default setting 0,06V to 0.648V seemed to solve the issue

0 Adam Sidelsky over 5 years ago in reply to Richard Bovenkerk

TI__Guru 62730 points

Richard,

I recommend checking the GHx, GLx, and SHx pins on a scope to check if there is any ringing or unexpected signals are seen. This will help us debug further.

Regards,

-Adam

0 Richard Bovenkerk over 5 years ago in reply to Adam Sidelsky

Prodigy 70 points

Hey Adam,

Did as requested. Here I made a PDF with the relevant scope images.

With the original design I see some ringing. But with the new design there seems to be a lot more.
I can imagine this would indeed trip the overcurrent feature.

Also it seems that GL_A is 0V for a short moment. Any thoughts on this?

Curious what you think about this.

0 Richard Bovenkerk over 5 years ago in reply to Richard Bovenkerk

Prodigy 70 points

Hey Adam,

The first link expired. Here are the scope images again.

Any idea on this?

https://we.tl/t-2oxle7y8zv

0 Adam Sidelsky over 5 years ago in reply to Richard Bovenkerk

TI__Guru 62730 points

Richard,

I cannot access file sharing sites, please use the image upload on the E2E post page.

Regards,

-Adam

0 Richard Bovenkerk over 5 years ago in reply to Adam Sidelsky

Prodigy 70 points

I hope these images are sufficient.

0 Adam Sidelsky over 5 years ago in reply to Richard Bovenkerk

TI__Guru 62730 points

Richard,

The new FET is about 1/3 the Qgd of the old FET. This Qgd represents the capacitance that the DRV needs to charge or discharge to turn the FET on or off. At 1/3 the Qgd of the old FET, the new FET is being turned on/off too strong and this is causing the gate/source to oscillate. I would reduce your programmed drive strength using register 0x02, bits D0 and D1 until you see this behavior reduce/eliminated.

Regards,

-Adam

0 Richard Bovenkerk over 5 years ago in reply to Adam Sidelsky

Prodigy 70 points

Thanks for the suggestion. Will try it as soon as possible.

Regards,
Richard

0 Richard Bovenkerk over 5 years ago in reply to Richard Bovenkerk

Prodigy 70 points

Hey Adam, Have been absent for a while and Iam back testing this.

I played around with this setting. This has no visible effect on the Ringing. 1900, 750 and 250ma. Ringing looked the same.
Then I changed the fet gate resistance I was able to reduce the Ringing greatly. The ringing looks better now than the Original used fet.

But my original issue remains. When I put the VDS on 20 it seems to work (not super stable but most of the time).
What suprises me, when I set OCP_MODE to OC disabled it does not seems to have effect.

I would expect setting this OCP_MODE to OC to disabled would ignore any VDS value. But this is not the case.
Any thought why OCP_MODE OC setting has no effect but VDS 20 setting has?

Regards,
Richard

0 Adam Sidelsky over 5 years ago in reply to Richard Bovenkerk

TI__Guru 62730 points

Richard,

Please check the Drain-to-source voltage of all FETs, I suspect there you will find an issue which then needs to be sorted out on the board.

Please post your waveforms and I will review the VDS.

Regards,

-Adam

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DRV8301: Overcurrent protection and VDS register settings