DRV8308: Ocassional Start Up Issue and Error Code Explanation

Robert Gilmore

Part Number: DRV8308

Occasionally a motor controlled by DRV8308 will fail to start, but when pushed slightly or moved to another location, it will start up.

Here is the schematic:

When looking at the fault code register 0x2A, we sometimes get 64, sometimes 80 and sometimes 16.

16 looks like a charge pump error, what should the scope plots look like on CP1, CP2 and VCP?

What is 64/80, these seem to be in the RSVD area.

Any other comments or improvements on our schematic are welcome, or what might cause this start up issue. If the motor starts it operates well with no issue on speed control.

over 2 years ago

0 Aaron Barrera over 2 years ago

TI__Mastermind 26046 points

Hi Robert,

We will get you a reply on Monday as today is a TI Holiday.

Thanks,
Aaron

0 Robert Gilmore over 2 years ago in reply to Aaron Barrera

Prodigy 20 points

Thank you.

One thing i'm going to try is increasing C68 to a 35V rated part. I'm not confident that will have any impact.

0 Aaron Barrera over 2 years ago in reply to Robert Gilmore

TI__Mastermind 26046 points

Hi Robert,

Not sure what 64 is (bit 16) since its reserved, I'll ignore it for now as it may be related to CPFAIL (charge pump undervoltage).

I think the issue is the VCP-VM charge pump cap (C58), it is rated for 10V. We recommend this cap to be rated for 25 or 35V, as VCP produces 10V above VM. Using a 10V rated cap will affect the rated capacitance of the part and dissipate the charge pump stored voltage quickly.

Thanks,
Aaron

0 Robert Gilmore over 2 years ago in reply to Aaron Barrera

Prodigy 20 points

Hi, I tried changing C68 (not C58 as you stated in your previous email) to a 50V rated part. The same fault was present when the motor was in the same position of starting as previously. I.e. 64 in the fault register followed by 80.

Do you have any more thoughts or need any more information to assist us with this?

The voltage at pin 28 of the IC according to my oscilloscope is: min - 20.9V max - 23.1V.

The voltage on the other side of C68 is: min - 11.3V max - 13.1V.

0 Aaron Barrera over 2 years ago in reply to Robert Gilmore

TI__Mastermind 26046 points

Hi Robert,

Does this issue happen across multiple devices or PCBs? Have you done an ABA swap to determine if the issue is a device issue or application issue?

Is the motor tuning correct? You can refer to section 4 of the user's guide for the DRV8308EVM: https://www.ti.com/lit/pdf/slvua41f

Have you tried using lower IDRIVE settings?

Thanks,

Aaron

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DRV8308: Ocassional Start Up Issue and Error Code Explanation