DRV8316C: Buck Converter OCP

Juliana Kampf

Part Number: DRV8316C

Tool/software:

Dear TI-Team,

I am currently evaluating the driver in my own design, but unfortunately, I have encountered a problem and need your assistance.

Every time I start my board, the status register reports a Buck Converter overcurrent fault. When I clear the fault using Clear Fault, the issue doesn't reappear.

The Buck Converter circuit can be seen here:

I am reading the following registers:

On the oscilloscope, I measure the following signals:

Pink represents the driver's power-up behavior.
Yellow shows the power supply voltage.
Blue indicates the startup behavior of the Buck Converter.
Green represents the current from the power supply.

Is this behavior characteristic of the driver?

Best regards,

Juliana

3 months ago

0 Yara Al Shami 3 months ago

TI__Expert 8895 points

Hi Juliana,

There is a pretty large spike in the current from your power supply. That could definitely be the reason why you are seeing a Buck over current fault. You can confirm this by probing nFAULT and seeing if the fault is triggered around that spike.

Regards,

Yara

0 Juliana Kampf 3 months ago in reply to Yara Al Shami

Prodigy 10 points

Hello Yara,

thanks for the quick response. The nFault pin is indeed triggered around the current spike.

Please ignore the initial spikes during startup. This board does not have any current limiting. The second spike is likely causing the OCP fault as soon as the driver and the buck converter start. Do you have any idea why this spike might occur when the driver powers up?

Best regards,

Juliana

0 Anthony Lodi 3 months ago in reply to Juliana Kampf

TI__Mastermind 22216 points

Hi Juliana,

Thanks for the updated data! Yara is out of office and will be returning next week. She should be able to provide an update by the end of next week.

Regards,

Anthony Lodi

0 Yara Al Shami 3 months ago in reply to Anthony Lodi

TI__Expert 8895 points

Hi Juliana,

You could try increasing your bulk capacitance?

looks like from your schematic you only have 100nF?

Regards,

Yara

0 Juliana Kampf 3 months ago in reply to Yara Al Shami

Prodigy 10 points

Hi Yara,

my Cvm1 capacitor is 100nF as recommended by TI, and Cvm2 is also larger than 10µF, considering the DC bias.

Regards,

Juliana

0 Yara Al Shami 2 months ago in reply to Juliana Kampf

TI__Expert 8895 points

Hi Juliana,

I'll look into this further and provide and update by the end of the week.

Regards,

Yara

0 Yara Al Shami 2 months ago in reply to Yara Al Shami

TI__Expert 8895 points

Hi Juliana,

I consulted some teams mates and concluded that it might be a good idea to increase your bulk capacitance, often times it take some trial and error to figure out what bulk capacitance might be too little or too much for your system. Is this possible to test in your current design?

Regards,

Yara

0 Juliana Kampf 2 months ago in reply to Yara Al Shami

Prodigy 10 points

Hi Yara,

thank you for your response. Yes, I have already taken measurements with higher capacitance. I added an additional 60µF, but unfortunately, the peak was not significantly lower (~300mA less).

I also took a measurement directly at the driver's input (VM). The current peak at power-on is much higher there. According to the datasheet, the buck regulator reports an overcurrent at 2A, and I am significantly exceeding this value.

But if an additional 60µF only reduces the current peak by such a small amount, the bulk capacitance would need to be very very large?

Regards,

Juliana

0 Yara Al Shami 2 months ago in reply to Juliana Kampf

TI__Expert 8895 points

Hi Juliana,

Where is the location of these capacitors in relation to the driver? There could be a possibility that your layout is allowing this spike to happen and the added capacitance isn't really helping.

Regards,

Yara

0 Juliana Kampf 2 months ago in reply to Yara Al Shami

Prodigy 10 points

Hi Yara,

the capacitors are located directly near the driver input.

Regards,

Juliana

0 Yara Al Shami 2 months ago in reply to Juliana Kampf

TI__Expert 8895 points

Hi Juliana,

Sounds like you have your capacitors in the right spot. I think you'll really just have to size up on your bulk capacitance unfortunately. Here is a app note that might help with that: https://www.ti.com/lit/an/slvaft0/slvaft0.pdf?ts=1727971232564&ref_url=https%253A%252F%252Fwww.google.com%252F

Regards,

Yara

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DRV8316C: Buck Converter OCP