DRV8308: DRV8308 burning at power supply

Peter Mirtschink

Part Number: DRV8308

Dear TI-Team and friends,

since some time we use the DRV8308 at an 18 Volt BLDC motor. Sometimes (less then 1% of your PCBs) we see burning parts and pins on the DRV. Please see attached picture.

What could be the problem here and how could we try to avoid this? On our MOSFET we use TVS diodes and power supply will not be higher then 21 Volt. The Predrive Current is set to 100 mA.

Thank you for help.

Peter

over 2 years ago

+1 Matt Hein over 2 years ago

TI__Mastermind 21805 points

Hello Peter,

I have a few questions:

What is the voltage rating of C8?
What is the voltage rating of C21?
What PWM frequency have you configured in the DRV8308? (these are very large MOSFETs and so the DC current consumption from the charge pump is quite high)
I noticed the ISEN pin is grounded rather than being shorted to I_MESS is this intentional?

Some preliminary comments:

The damage location seems to be located around VCP/VM on the device. We see that this type of damage is most common when there is an over voltage event
While the TVS diode begins to clamp at ~21V, the maximum clamping voltage is 29.2V @ 20.6A. It is possible that the TVS will clamp at 21-29V depending on the motor current.
- Your VM bulk capacitor is only rated to 25V, meaning it will likely have much less real capacitance when biased at 18V (see this article)
- I would recommend using at least 35V rated components (2x the nominal voltage)

Thanks,

Matt

0 Peter Mirtschink over 2 years ago in reply to Matt Hein

Prodigy 220 points

Hi Matt,

the Voltageratings I will Reply tomorrow. But maybe the first important information, the PWM frequency is 25 KHz.

ISEN is shorted because the current is measured at the power supply.

Regards Peter

0 Matt Hein over 2 years ago in reply to Peter Mirtschink

TI__Mastermind 21805 points

Hi Peter,

I wouldn't recommend going higher than 25kHz on the PWM frequency. You may want to check to make sure the part is not getting too hot due to charge pump and low-side gate drive voltage loading. There could be a situation where the MOSFETs on the 1% of boards are on the high end of Qg distribution - can you check this?

Thanks,

Matt

0 Peter Mirtschink over 2 years ago in reply to Matt Hein

Prodigy 220 points

Hi Matt,

I have higher the PWM to 50 kHz. I don't see any problem until now. At 100 kHz the motor is nor running.

Here the missing values to voltage rating:

C8 - 50V

C21 - 50V

I will check if we can higher the voltage of the VM Bulk capacitor.

Thanks, Peter

0 Matt Hein over 2 years ago in reply to Peter Mirtschink

TI__Mastermind 21805 points

Hi Peter,

Those capacitor voltage ranges look good. 50V should be enough for C8 & C21.

Thanks,

Matt

0 Peter Mirtschink over 2 years ago in reply to Matt Hein

Prodigy 220 points

Hi Matt,

thank you. We will try to higher the voltage of the bulk capacitor and let it run with 50kHz. After some weeks we should see if there is any problem again.

Thank you!

Regards Peter

0 Matt Hein over 2 years ago in reply to Peter Mirtschink

TI__Mastermind 21805 points

Hi Peter,

That sounds good. I will close this thread for now but please feel free to post additional questions if you have them!

Thanks,

Matt

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DRV8308: DRV8308 burning at power supply