DRV8424: Reverse current spikes at sine peak in Smart Tune Ripple Control mode.

Jim McGarvey

Part Number: DRV8424

Using DRV8424 per schematic below. All datasheet layout guidelines are followed. VM = 6 to 8V.

PRI_MTR_M0 is driven low for 1/32 and hi-z for 1/256 (with pullup to DVDD).

In both 1/32 and 1/256 mode and at lower currents (controlled by PWM input to VREF), I see reverse current spikes at the peak of the sine wave, for one STEP pulse duration.

Top scope shot is current to motor. Spikes are only on B outputs, and occur randomly, like popcorn. Lower scope shot shows spike relative to STEP input.

Problem only occurs in Smart Tune Ripple Control mode (DECAY1 = 1). When DECAY1 = 0, I don't see the spikes.

M1 is open on the board and measures 2.0V as it should in Hi-Z. I don't see it changing on the scope.

DIR = 0 or 1. EN, SLEEPn = 1. TOFF = 0 or 1. DECAY0 = 0.

Spikes are less frequent as I increase motor current. Above ~0.5 amp, I don't see them.

over 4 years ago

0 Wang5577 over 4 years ago

TI__Guru 56650 points

Jim,

Thank you for sharing such detail waveforms. Only the full step setting can make the output current changing that much in one step. But, the M0 and M1 setting are both different between full step setting to 1/16 or 1/256 micro-stepping setting.

Let me check it on my bench. Also, would you help me slow down the STEP pulse frequency? I want to check the output current goes to a random number or stabilize at a full step current setting. BTW, do you have an EVM?

Regards,

Wang Li

0 Jim McGarvey over 4 years ago in reply to Wang5577

Intellectual 490 points

Thanks, Wang.

I do have an EVM. I will try it with very slow stepping and let you know shortly.

This part in the data sheet made me think the reversing of the bridge is the problem, since DECAY mode affects it.

In fast decay mode, once the PWM chopping current level has been reached, the H-bridge reverses
state to allow winding current to flow in a reverse direction. The opposite FETs are turned on; as the winding
current approaches zero, the bridge is disabled to prevent any reverse current flow

0 Jim McGarvey over 4 years ago in reply to Wang5577

Intellectual 490 points

Here's the waveform at 16 msec per step. The current is settling at ~1.9A (scale is 185mV/A). VREF is 0.22V so full scale current should be 0.17A.

EDIT: Scope was AC coupled, so levels are misleading. Settled current is really ~2.1A.

ALSO.. this is still on my board, not the EVM.

0 Wang5577 over 4 years ago in reply to Jim McGarvey

TI__Guru 56650 points

Jim,

I just duplicated this issue on my bench. Let me discuss it with our design engineer to find out the root cause. When I have the detail info, I will let you know ASAP.

Thanks,

Wang Li

0 Jim McGarvey over 4 years ago in reply to Wang5577

Intellectual 490 points

That's good news. Thanks, Wang.

0 Wang5577 over 4 years ago in reply to Jim McGarvey

TI__Guru 56650 points

JIm,

Our designer works on it. Let me put this thread temporary close. When I have the update, I will reopen it and post the update.

Regards,

Wang Li

0 Wang5577 over 4 years ago in reply to Wang5577

TI__Guru 56650 points

Jim,

Sorry, the designer is busy this week. I hope we can have a result next week.

Regards,

Wang Li

0 Jim McGarvey over 4 years ago in reply to Wang5577

Intellectual 490 points

Thanks, Wang. I'm looking forward to understanding!

0 Wang5577 over 4 years ago in reply to Jim McGarvey

TI__Guru 56650 points

Thanks for your patience.

0 Wang5577 over 4 years ago in reply to Wang5577

TI__Guru 56650 points

Jim,

Last week, design and validation team cannot duplicate on their bench. We had a webex meeting to show my bench waveforms. Now, they understand the issue. But, it would take them more time to find the root cause.

Thanks,

Wang

0 Wang5577 over 4 years ago in reply to Wang5577

TI__Guru 56650 points

Jim,

Design team has an internal review for this issue. The report will be release soon.

Regards,

Wang Li

0 Jim McGarvey over 4 years ago in reply to Wang5577

Intellectual 490 points

Thanks for keeping track of this, Wang!

0 Wang5577 over 4 years ago in reply to Jim McGarvey

TI__Guru 56650 points

Jim,

I just sent you a private message to discuss this issue.

Regards,

Wang Li

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DRV8424: Reverse current spikes at sine peak in Smart Tune Ripple Control mode.