DRV8251EVM: voltage peak while break/coast

Julian Wienold

Part Number: DRV8251EVM
Other Parts Discussed in Thread: DRV8251

Dear support,

i´ve got a question about the DRV8251EVM.

When the dc motor is running (foreward or backward) and i switch to break or coast, the supply voltage (yellow) is drifting away.

The voltage peak is around 5 volts and causes the DRV8251 to stop working (motor is not running but i can measure pwm at IN1 and IN2). I have to cycle power to get it back running.

This also happens when i use the internal pwm module on the drv8251evm.

Supply voltage is 12 V and the dc motor draws around 1.4 to 1.6 Amps.

I use pwm signals from an external microcontroller. The frequency is around 31 kHz.

Is there anything wrong with my supply voltage or is the dc motor just to big for the drv8251?

best regards

Julian

over 1 year ago

+1 Ryan Kehr over 1 year ago

TI__Guru 54695 points

Julian,

I believe this is what you are seeing:

https://e2e.ti.com/blogs_/b/industrial_strength/posts/art-of-stopping-the-motor-vm-pumping

Suggestions for how to deal with this issue are in the link above.

Regards,

Ryan

0 Julian Wienold over 1 year ago in reply to Ryan Kehr

Prodigy 10 points

Hi,

thanks for your help. I´ll check it out.

But why are the outputs disabled?

VM does not exceed the maximum ratings. Is this caused by the OCP?

Regards,

Julian

0 Ryan Kehr over 1 year ago in reply to Julian Wienold

TI__Guru 54695 points

Julian,

If you have to cycle power or cycle nSLEEP, the fault is likely OCP.

Regards,

Ryan

0 Julian Wienold over 1 year ago in reply to Ryan Kehr

Prodigy 10 points

Hi Ryan,

i think, this explains, why i can measure the voltage peak even while using break mode

motor runs -> break mode -> OCP will be triggered -> disable H-bridge -> coast mode -> vm pumping

So i will reduce the dutycycle slowly to avoid OCP.

I want to prevent damage to other circuits in fault condition

Does it make sense to use TVS diodes (in parallel to C bulk) to reduce this voltage peak?

Regards,

Julian

+1 Ryan Kehr over 1 year ago in reply to Julian Wienold

TI__Guru 54695 points

Julian,

I think your description above is an accurate representation of what is happening.

Either TVS or increasing bulk cap are effective to limit this vm pumping condition. A combination of the both is often used.

Regards,

Ryan

0 Julian Wienold over 1 year ago in reply to Ryan Kehr

Prodigy 10 points

Thank you for your support

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DRV8251EVM: voltage peak while break/coast