DRV8305-Q1: DRV8305NEPHPRQ1

Hi Mohammad,

Can you clarify the procedure that led up to you noticing the chip was damaged? Was the device driving a motor at 150C? is only one Phase damaged?

Regards,

Michael

Hi Michael,

Sure, please let me know what specifically you would be interested in knowing? I will attempt to explain our procedure for the testing.

This specific testing for the unit entails changing in the Supply voltage, Torque, and % change in Torque (from 90% to 10%, 10% to 90%, 20 to -20%, -20% to 20%) cycled over a 5 min duration at 150C ambient thru out. We record the temp from the EEPROM data. The Supply voltage is 27.6V, and 36V. Torque is 1.35Nm and 2.2Nm. This entire test is performed over a 2 hour duration. 

During testing, at 150C ambient, with this unit, we recorded 172C on the EEPROM which resulted in the unit failing and not starting back up. Other units continue to run during testing. We are examining other reasons that maybe resulting in one of the "V" phases failing in the motor. Such as grease contamination getting cooked on the 29 -32 pins and causing a low resistance path for one of the phases. 

However, we continue to suspect Pins 29-32 in the DRV8305 as the primary contender for the failure of this unit.

Please shed some more light on the DRV8305 internal workings that maybe resulting in this. We may eventually reach out to TI for a failure analysis of the chip to better understand as we have seen a failure of the chip from TI in the past.

Please provide ASAP.

Thank you

Mohammad

Correction the unit is soaked in 150C for 2 hours and then placed in room ambient temp.

Please include answers to all previous queries asked. Thank you.

Hi Mohammad,

This could have been caused by an external short like the high side or low side FET failing. Can you check the continuity of the pins 29-32 to Vm and GND to see if there is a short. To understand how the drivers work you can look at section 7.3.5 of the datasheet.

Regards,

Michael 

Hi Michael,

We have already measured pins 29-32  to Vm and GND and have seen a lower resistance than typical of the low side complementary FET. So we are not certain whether pins 29-32 on the DRV8305 are still functioning. Is there anything from an internal workings, from your experience and knowledge, that would cause those pins to malfunction or not work at all?

It appears there may have been grease applied to the gear that got "cooked" on pins 29-32 that essentially caused a partial or full short. Once residual analysis was performed, there has been a correction. However, we are not certain this resolves the issues. For this reason we are re-assembling the unit and will try to re-run if it re-runs in typical manner.

Thanks for your support.

Mohammad

Hi Mohammad,

What I suspect might have happened from your description so far is that the grease could have shorted something on our device for example PVDD and GLB. This caused internally to our devices the metal traces to melt and contact each other. I have not come across a scenario like this before. 

swapping the unit and retesting the board while preventing grease to get on the board should fix the issue.

Regards,

Michael W.

Hi Michael,

Shorting of the internal pins is what we suspected due to the grease as well. However, when we removed some of the "crusty cooked" grease on the pins and powered it up the fault went away. Now when we try to re-create the error with the same grease cooked up to 170C on the same pins the problem does not show itself.

We are not sure what might have happened that is causing this inside of our actuator application. Any thoughts or experiences that could be shared here?

We are looking at a couple of other scenarios as well.

Please let us know of your thoughts.

Thanks

Mohammad