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DRV8308: Motor Driver MOSFET selection

Part Number: DRV8308
Other Parts Discussed in Thread: CSD88537ND

Hi everyone, second post.

I am currently in the process of designing a BLDC motor driver. I did ask another (unanswered as of posting of this question) question about this motor driver for the hall effect sensors but have come across another problem. I would like to know how I'd go about choosing the MOSFET's for the motor driver. The datasheet of the DRV8308 is below but I couldn't spot anything regarding the selection of the MOSFETS. I did find a reference schematic and it uses a CSD88537ND dual MOSFET chip. I'm not too sure that would suit the motor type that I am targeting (https://hobbyking.com/en_us/turnigy-aerodrive-sk3-4250-350kv-brushless-outrunner-motor.html). Any response and help would be appreciated and thank you for your time!

The DRV8308 datasheet: DRV8308 Brushless DC Motor Controller datasheet (Rev. B) (ti.com)

 
  • Hi Jeeva,

    The MOSFET needs to be selected to support the maximum current (RMS and peak) that you are trying to drive. In general, most gate drivers can drive most MOSFETs.

    A gate driver has a certain maximum gate drive current - in the case of DRV8308 it is 130mA. Your MOSFET rise time will be dictated by the gate drive current you configure, rise time is approximately equal to Qgd / IDRIVE. We normally recommend 100-300ns rise time as a target. You will adjust the gate drive setting in the device and potentially add additional series resistors externally to further limit the output current into the MOSFET gate. If you have a really, really small MOSFET, you want a small gate drive current to get to 100-300ns. If you have a huge MOSFET, you will need quite a bit more gate drive current to get to 100-300ns, or even have to settle for a longer rise time.

    By the way, that motor will want to spin at a very high speed, and likely will want a trapezoidal control scheme. I'm not sure if DRV8308 will be well suited for it given that the motor itself does not have any sensors integrated into it. So my guess is that you need something that is sensorless trapezoidal (i.e. this reference design)

    Thanks,

    Matt