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DRV8343-Q1: Configuration Issues

Isaac Sundin
Prodigy 20 points
Part Number: DRV8343-Q1

We are having an issue integrating our DRV8343 in a 3phase BLDC motor configuration.
We have now had two instances where we believe we have our software configuration set up, we are able to drive each Phase individually with a resistive load, and the High Side and Low Side seem to be functioning properly. However, when we go to actually try driving a 3 Phase Motor with hall-effect/state feedbacks we somehow have managed to blow the chip.

After reviewing the power stage circuit from the DRV8343X-Q1EVM schematics (MD005A(001)) I noticed that there is a 330uF Capacitor in parallel with a 1uF and 10nF capacitor. We do not currently have a capacitor on the Drain of the High Side of the power stage FETs. Would you expect that there would be some sort of inductive feedback from the motor that would cause a feedback into the DRV8343 that could damage it without the presence of this large electrolytic (330uF)? That looks to be the only difference between our design and the evaluation board so I'm just wanting to know if perhaps there is something else I may be missing with our setup.

Also, we do have a main power relay architecture that self protects (turns off VM) when there is an over-voltage condition of 36V or greater. If this turned off because there was a load dump/transient spike, could this be a potential cause of VM trying to find a return path through the DRV8343.

Thanks in advance.

  • 0
    Prodigy 20 points

    I read in another post that "all capacitors listed in the datasheet are needed". But in the actual DRV8343-Q1 datasheet there are no capacitors on the Drain side of the High-Side FETs so we did not see a need to put them but on the Eval board schematics (EVM) they did. If these capacitors are needed, then I think the datasheet block diagrams need updated to include these.

    Just to reiterate. Our schematics look like the Functional block diagram as seen on page 19 in the datasheet. Our Rsense is 5mOhm. 

    Also, we were curious if there needed to be a series gate resistor or a gate to source resistor. We have seen these on other designs and have tested it with both with the same results of a damaged chip.

  • +1 in reply to Isaac Sundin
    TI__Expert 3535 points

    Hi Isaac,

    The capacitors on the high side drain

    These are the decoupling and bulk caps. The capacitors primary purpose is to provide charge to the system so the main supply, VM, doesn't have to. The small value capacitors can be charged up and emptied very quickly whereas the larger capacitor can store a lot of energy, however they won't react as quickly.  Because the cap values can provide some charge quickly and a lot of charge over time, it helps with ringing and the initial spikes seen in a system. It is highly recommended to always use them. A few 100uF to 330uF caps in parallel with a few 1uF to 2.2uF is a good starting point with some more footprints that can be added later.

    If there is a point where to motor starts acting like a generator, then yes there can be a current that flows into the supply. Having those capacitors there will store that energy instead of causing VDRAIN to rise to a higher than abs max of the device which can blow the IC.

    Series gate resistor

    We recommend if you're using a part with IDRIVE, use a 0 ohm as a placeholder and then test the system. Then increase the resistance if you need an in-between slew rate (between two IDRIVE settings) or if you want to make it slower, in general. 

    I hope this helps, let me know if you have any follow up questions


    Thanks,

    Michael