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Copper area for DRV8312

Matthew Brown
Prodigy 90 points
Other Parts Discussed in Thread: DRV8312, TPA3004D2

I'm designing with the DRV8312 which includes a PowerPAD.   How do I determine the amount of copper area required for a given amount of power dissipation? 

I see in SLMA002, you include a table that list different ThetaJA values for "TI Recommend Boards".  I've read the layout consideration (which were very helpful), but I don't see any modeling or estimation for copper size on the PCB?

Any pointers would be great!

Thanks.

Matt

  • 0
    TI__Guru 55615 points

    Matt,

     

    We don't have any numbers specifically for the DRV8312, but we have collected data for a package that has a similar exposed power pad.  From the data in the following datasheet starting on page 32, you can get an approximate idea of how the theta-ja number scales with copper area on a 2-layer vs. 4-layer board.  There is also an example calculation.

    http://focus.ti.com/lit/ds/symlink/tpa3004d2.pdf

    Regards,

     

    Ryan

     

  • 0 in reply to Ryan Kehr
    Prodigy 90 points

    Thanks Ryan - the thermal resistance vs. copper area curves in that datasheet are great.

    I noticed that the TPA3004D2 lists an "operating junction temperature" recommendation. 

    The DRV8312 only specs an absolute maximum junction temperature.  By definition this is not the number I should design to for best long term device reliability.   Is there a recommended operating junction temp for this device?

     

    Thanks,

    Matt

  • 0 in reply to Matthew Brown
    TI__Guru 55615 points

    Matt,

     

    The device is reliable up to 150C junction and thermal protection will protect the device (disable the outputs) at temperatures above this.  

     

    There is a nice feature on the DRV8312 that gives you a "thermal warning" output on the /OTW terminal.  This thermal warning is at ~125C.  You can monitor this with your micro and ensure that the outputs are never disabled by throttling back on the speed or torque when you hit thermal warning.  

     

    Basically, I would suggest designing your system to ensure you are not going into thermal trip and causing discontinuous operation.  With the internal protections in the device, it will operate reliably up to 150C.