CSD19532Q5B: CSD19532Q5B

Hello Mika,
Thank you for posting!

For starters I would refer you to these two blogs written by my colleague Manu Balakrishnan as a primer:

e2e.ti.com/.../optimized-thermal-design-for-three-phase-motor-drives-in-power-tools-part-1
e2e.ti.com/.../optimized-thermal-design-for-three-phase-motor-drives-in-power-tools-part-2

Manu does a pretty great job explaining how to minimize the thermal impedance of the FETs to the ambient environment, thus maximizing the amount of current the FETs can drive. The device he uses in the example, the CSD18540Q5B, has very similar thermal characteristics to the 100V CSD19532Q5B you have selected.

The second blog in particular gives some excellent suggestions for dealing with SMT devices like TI's SON5x6. Here is an excerpt.

"Here are a few important points to consider for good thermal design of a printed circuit board (PCB):

Provide large copper planes in the PCB. Solder the exposed pad of the device to the copper plane and extend the plane to the edges of the PCB in order to increase the heat-spreading area. With a four-layer board, you can use copper planes in all of the layers to spread the heat, which in turn can give up to 30% improved performance compared to a two-layer board. The larger the PCB area, the higher the heat dissipation due to convection. Provide the copper planes without any breaks so that the heat spreading through the planes will be efficient.

Lower thermal resistance with multiple vias. Provide as many thermal vias as possible underneath the device case and connect the vias to the copper planes in all the layers. A typical 12mil diameter through-hole via with 0.5oz copper sidewalls has a thermal resistance of 261°C/W. Completely filling the vias with copper can bring down the thermal resistance by as much as half; however, this technology may double the cost of the PCB. A more economical option is to provide 1oz plating on standard 12mil vias, which would add only a 10-20% additional cost. This can help bring the thermal resistance of a single via to 140°C/W.

Copper thickness: by increasing the copper thickness of the copper planes, more heat transfers laterally, helping to spread heat to the entire PCB. Increasing the thickness of copper increases PCB cost; however, 2oz copper thickness is a good choice for power-tool applications where there is a size constraint on the PCB. By increasing the copper thickness from 1oz to 2oz, you can achieve up to a 25% increase in thermal performance."

Hopefully this answers your question but if you have further inquires after giving those a read (particularly part 2), please let me know and I will be happy to help.