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DRV8301: DC-Link Capacitor Sizing

Pranit Pawar1
Prodigy 50 points
Part Number: DRV8301

Hi Experts,

I'm trying to figure out how to size DC-Link capacitance for motor controller. Most of the literature considers current and voltage ripple to get value of C. However, I'm looking for practical design, i.e. considering a dynamic loads, ESR, temp and lifetime variations. A graphical representation of my query - 

Any references/papers/videos/practical designs would be appreciated. How is capacitor sizing done in the industry? Just a preliminary analysis showed that theoretical approach might get convoluted. So I was wondering what are the widespread practices in the industry and the success of designs based on these practices?

  • 0
    TI__Mastermind 23045 points

    Hello Pranit,

    Thank you for posting to the MD forum. Just to clarify, when you say DC Link capacitance are you referring to the capacitance that is placed in parallel with the power supply of your system.

    If this is the case we do have a TI Precision Labs video that I believe may help you out: https://training.ti.com/ti-precision-labs-motor-drivers-voltage-margin-and-bulk-capacitance

    Let me know if this helps address your question.

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Prodigy 50 points

    Hi Isaac,

    Yes, DC-Link capacitor (or bus capacitor) is the capacitance placed across my power supply (in my case, battery). The video mentioned in your reply provides a generic answer. I'm looking for specifics, few in-depth technical insights and guidelines. How to size the DC-Link capacitor in varying ambient temp environment considering current stress, ESR, lifetime and their variation with capacitor core temperature.

    I'm seeking practical design guidelines/considerations, tried-and-tested rules of thumb used in the industry. Yes, one can approach the problem with lengthy calculations and design theoretically. But the gains obtained by that, given the time investment and complexity, might not be significant when compared to a more practical, rule-of-thumb based design. Hence my query

  • 0 in reply to Pranit Pawar1
    TI__Mastermind 23045 points

    Hello Pranit,

    Thank you for confirming what you meant by DC-Link. Unfortunately, we can only provide a rough calculation via the equation on the video linked above. This is a good rule of thumb or starting point to calculate bulk capacitance for your system. Other than that we typically recommend using X7R capacitors since they have a smaller variance under heat, and using AEC qualified components since they guarantee a certain level of quality and reliability.

    DC-Link capacitance can be a trial and error process but the formula provided is a great starting point. On another note, a lot of the questions feel aimed towards a capacitors behavior in their lifetime, something in which we are not experts on, this would be great questions to check with a capacitor manufacturer since they would have further comments on the longevity of the capacitor throughout its life and how it might be affected by other factors you mentioned over time. I hope this helps!

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Prodigy 50 points

    Yes I understand Isaac that capacitors isn't TI's forte. But could anyone from the motor control team help? There are many motor controller ref designs, so maybe someone from there could be able to help me out?

  • +1 in reply to Pranit Pawar1
    TI__Mastermind 23045 points

    Hey Pranit,

    I am part of the motor control team, the reference designs we make typically follow the recommendations we make in the data sheet. The datasheet will typically contain a recommendations on the pin functions section or a table in an external component sections (examples below for other devices, not DRV8301).  These suggestions are conventionally tailored for each device, factoring voltage tolerances and other device specifics.

    We make these suggestions across various use cases and across various industries everyday, and usually with a high success rate. As mentioned earlier bulk capacitance can be a trial and error process, if you have an application where your system will be in abnormal/high stress conditions then this might require some additional testing.

    Regarding these questions:

    Pranit Pawar1 said:
    How to size the DC-Link capacitor in varying ambient temp environment considering current stress, ESR, lifetime and their variation with capacitor core temperature.

    I still believe that a capacitor manufacturer can answer these questions better than we can. We make value suggestions that you can follow, but if the advertised value of the capacitor is affected by the points mentioned above, then the manufacturer should be able to make suggestions on how to reduce these effects or recommend other products that can help you achieve stability in these cases.

    Best,

    Isaac 

  • 0 in reply to Isaac Lara
    Prodigy 50 points

    Will catch up with manufacturer because the application certainly demands additional information and testing .But, thanks Isaac for the clarification!

  • 0 in reply to Pranit Pawar1
    TI__Mastermind 23045 points

    Hello Pranit,

    I hope we were able to help. Let me know if you have any other questions!

    Best,

    Isaac