DRV8711: Fault with DRV8711 when motor slips

Just a quick update. After examining PCB, noticed DRV8711 failed.

Hello,

Where do you put the Zener diode? Is it on VM bus? How many capacitors do you put on VM bus?

If you can use a scope to capture the voltage spike, that can help us to find the root cause.

If the motor accelerates due to the heavy load and damages FETs and driver which you believe it is because of BackEMF. Basically, we need a clamp circuit to quickly response the high voltage spike on VM bus and that clamp circuit can absorb the energy sending back from the motor.

I would think we may need to update the clamp circuit: when the input voltage is higher than a certain level, turn on a switch on VM bus and short the VM to ground through a load resistor and that switch.    

Hi Wang,

Thanks for your help. please see attached schematics of the driver. We also noticed that our processor board which in charge of controlling SPI bus also failed which leads to back EMF scenario. apprecite your comments

as you can see we have protection diodes on motor signals. A+ A- B+ B-

Vm doesnt have any diodes on that. what would be the recommended one? see also attached back EMF measured from motor in excess of 480V for period of over 300ms. Thanks

Hi,

You are experiencing regenerative breaking, for me circuit below works well for motors up to Nema34 in my prototype board.

Additionally electrolytic cap. between VM and GND,  about 1000uF for every ampere of motor current may be a good thing.

Best Regards,

Grzegorz

Hello,

The diodes on A+ A- B+ B- cannot clamp the VM voltage because those diodes don't absorb any energy when the VM voltage is higher than normal operating voltage.

So, we have to block the motor reverse spin; or design a clamp circuit to clamp the VM voltage (For example: https://patents.google.com/patent/US20110057627A1/en ).

Thanks guys for your support. we will go ahead with your valuable suggestions.