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DRV8301: Risks when running beyond maximum gate drive currents

Steven Shenker
Intellectual 860 points
Part Number: DRV8301
Other Parts Discussed in Thread: DRV8353

Hi there,

I have put together a motor controller board based on the DRV8301 where the mosfets gate charge combined with the desired running frequency exceeds the maximum average total output current of the DRV8301 which is 30 mA according to the data sheet.

My selected mosfet has 172 nC gate charge at 10V. My calculations for required drive currents for 6 mosfets at 48 kHz is  = 6 * 48 * 172 = 49.5 mA, exceeding the maximum output of the DRV8301s 30 mA.

When measuring the mosfet gate voltage I would have thought that because the DRV8301 cannot provide 49.5 mA average that the measured value would be lower (e.g around 6V) but it was still 10V. 

Is there any explanation for this? Does this mean that the DRV8301 is actually providing more current than stated in the datasheet? Will this cause damage to the DRV8301 over time? If it is not providing 49.5 mA then where would this effect be noticeable/measurable? Or am I missing something?

Many thanks! 

  • 0
    TI__Guru 63060 points

    Steven,

    Could you share your schematic with us?

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Intellectual 860 points

    Hi Adam, 

    Please find this attached. Note that this is designed for a 48V motor/battery.

     Many thanks,

    Steven

  • 0 in reply to Steven Shenker
    TI__Guru 63060 points

    Steven,

    What's your commutation method?

    For sine commutation or FOC this calculation may be correct because all three phases 6 FETs are switching most of the time. 

    For Trap commutation divide by 3 because roughly only 2 FETs are switching at a time so the load is much less on the charge pump.

    If you are really pulling 50mA then it's possible that the charge pump is working fine at this nominal condition. Our datasheet must be rated to cover the full voltage range and temperature range of the device so maybe there's a corner where it wouldn't work as well.

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Intellectual 860 points

    Hi Adam, 

    We are using Instaspin Motion which I assume is built on top of FOC? 

    Further update on this, we have now had 2 chip failures with the fault listed as GVDD low when reading from SPI. 

    My concern is that the drive currents are causing these failures. Do you know if this is possible? 

    If this is unrelated we may have to dig into our layout with you. I have also been seeing some false triggering of the OCTW as well as complete chip shutdown (identified by registers being reset to defaults). 

    More info on our application: We have an engine coupled to a motor and discharge the 48V battery during motoring, and charge the battery during generating. I am concerned that this chip may not be suitable for this application, barring any issues with our layout. Would it be possible to send you our layout directly to give it a once over?

    Do you think that the voltage tolerance of 60-65V of the DRV8301 is too low for our application? Should we be looking at something like the DRV8353?  

    Thanks in advance for your support,

    Steven

       

     

  • 0 in reply to Steven Shenker
    TI__Guru 63060 points

    Steven,

    You can send me an email about this.

    Typically 48V is a little close to the 60V limit of the DRV8301 but if you can control your system voltage to stay below 60V then you may be okay.

    Regards,

    -Adam