DRV8306EVM: Reg. Maximum operating current of the board

Hey Prasanth,

Thank you for posting your question to the E2E. I will consult the team and aim to provide feedback by Wednesday of next week.

Best Regards,

Akshay

Hi Prasanth, 

Also just chiming in quickly here to ask additional questions so that we may better understand the likely root cause

I think for the PCB current-rating consideration, this'll mainly be a matter of layout (trace thickness and GND planes) as well as individual component ratings as you've mentioned. 

• so we'll investigate further and share the conclusion over e2e

I also noticed that the C8 capacitor was removed (footprint is right next to the burned trace) - was this an intentional PCB modification? 

• I believe this is a bulk capacitor meant for MOSFET power stage VDRAIN to stabilize the voltage, so it definitely plays a crucial part in the overall system performance especially on matters of supply voltage pumping from motor transients
• so removing this cap may be the cause of the system-level damage. Can you also help provide some comments on other damage observed in the system? 

Resources: 

1. https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1041760/faq-how-to-not-damage-your-motor-drive-system-from-overvoltage
2. https://www.ti.com/lit/an/slvaf66/slvaf66.pdf

Best Regards, 
Andrew 

Thank you, Akshay

Hi Andrew, Thank you for information about the C8 Capacitor. I just removed it to get a detail picture of the burned trace. 

The trace was burning, while the capacitor was still soldered on as it is. (Do you think it could happen if there is short in the motor windings?)

I don't have an access to good multimeter to test out the motor windings. With the cheap multimeter I have, it shows a short circuit between the motor phases.

However, the board started acting different as i said in my initial post (nFault LED automatically lights up even if there is no motor connected and just powered the board). Maybe as you pointed out, the removal of the capacitor caused this issues. I replaced the capacitor back after taking a picture but still the board is not functioning. Maybe i should not have powered it without the bulk capacitor.

Thanks,

Prasanth

Hello Prasanth,

Thank you for your patience.

As Andrew mentioned, the bulk capacitor serves a crucial role in stabilizing the voltage.

Since you mentioned that the trace started burning before removing the capacitor, I am wondering if the current limit set on the supply was too high. What was the current limit you had used when the incident occurred.

I would recommend not using more than 10A.

If you have another EVM available, please try to run the motor using the lowest VDS and IDRIVE setting. I would also recommend not setting the speed potentiometer at the highest setting to try and diagnose what could have happened.

The motor phases short is expected and shouldn’t be the issue.

Hope this offers some clarification.

Best Regards,

Akshay

Hii Akshay,

Thank you for your inputs. 

The supply which I used doesn't have a current limit feature. However, The trace started to burn when I was testing with the lowest VDS and IDrive settings (Jumpers towards the edge of the EVM). I could see a little smoke from the burning of trace and soon the nFault would set. I feel I didn't even cross 50% of the potentiometer while this happened. 

I don't have an access to another EVM right now. I am just waiting to confirm the current rating of the EVM before ordering another one. 

Thanks,

Prasanth

Hey Prasanth,

I will consult the team and aim to provide feedback before the end of the week.

Best regards,

Akshay

Hey Prasanth,

The trace that got burned is only 10mil wide and I wouldn’t recommend passing more than 1 Amp through it. Most likely there is a short after the burn which caused a high amount of current to pass through the trace leading to failure. The following image shows potential areas where a short might have occurred. I would suggest using a multimeter to do a continuity test to see if there is short in the suggested areas leading to current to go straight from VM to Ground.

I hope this offers some insight.

Best Regards,

Akshay

Thank you, Akshay.

I will check for any shorts between those pins and update you.

Regards,

Prasanth.

Happy to help!

Best Regards,

Akshay

Hi Akshay, Thank you for you inputs.

I couldn't find any short between VM and GND.

However, I found a short between GHA and VM; Test point A and VM

I am not sure if it happened because of the fault on the motor side. Or maybe the FET has been damaged.

Could you recommend any other EVM for driving a 3 Phase BLDC motor (24V 20.1 AMP)?

Regards,

Prasanth

Sorry for the late reply, Akshay. I thought to give DRV8306EVM another try. I am ordering one today. I will keep you posted about how it goes.

Regards,

Prasanth

Hey Prasanth,

Thanks for letting me know.

Best Regards,

Akshay