DRV8874EVM: Ringing Observed at Falling Edge of OUT Signal

Jonathan Kong

Part Number: DRV8874EVM

Tool/software:

Hello TI Team,

I am using the DRV8874EVM connected to our motor with the specifications per below.

The EVM’s PMODE is configured to GND for PH/EN Control Mode, set up for single motor operation. The EVM board is powered by 24V. When I adjust the IN1 potentiometer, PWM signals begin, and the motor starts rotating.

I have observed a ringing signal occurring at the falling edge of the OUT1/OUT2 signal. This effect becomes particularly pronounced when the PWM duty cycle is set around 6.21%.

Kindly see below for the waveforms.

I tried removing R7 and replacing it with a 0-ohm resistor, but the ringing signal still persists.

Could you please advise on the possible causes for this ringing and recommend effective methods for its mitigation?

Motor Spec:

Waveforms:

Schematic:

2 months ago

0 David Medis 2 months ago

TI__Mastermind 21020 points

Hello,

Please allow me time to review. I'll reach out by tomorrow with an update.

Best,

David

0 David Medis 2 months ago

TI__Mastermind 21020 points

Hello,

From the image you shared it doesn't appear to be a normal "ringing" condition, the image on shows undershoot.

If possible, please provide another capture of this condition with VM. I'm curious what the supply voltage looks like during this condition.

Also, can you repeat these tests but with no load to see if this same behavior is present.

Best,

David

0 Jonathan Kong 2 months ago

Prodigy 25 points

Hello David,

Please find below the measured waveforms of VM, OUT, and the current of OUT.

During no-load condition:

Thank You

Regards
Jonathan

0 David Medis 2 months ago in reply to Jonathan Kong

TI__Mastermind 21020 points

Hi Jonathan,

What's the R/L or the brushed-DC motor?

The supply voltage is seeing a dip and causing ripples from the load. Could you try increasing the bulk capacitance?

Best,

David

0 Jonathan Kong 2 months ago

Prodigy 25 points

Hello David,

While I was checking the R/L of the brushed DC motor, I captured the output waveform after adding a 470 µF electrolytic capacitor in parallel with C1.

However, the dip is still present.

Waveform:

Schematic:

Thank You

Regards
Jonathan

0 David Medis 2 months ago in reply to Jonathan Kong

TI__Mastermind 21020 points

Hi Jonathan,

That's good news. I'm glad adding the bulk capacitance smoothed out the supply voltage.

The "dip" should go away when a load is attached. Have you tried testing with a load?

Best,

David

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DRV8874EVM: Ringing Observed at Falling Edge of OUT Signal