Вы плохой читатель

В примечании D к рисунку рекомендуемой разводки есть ссылка на документ SCBA017.
А в SCBA017 :
When thermal dissipation is crucial, the QFN package has an advantage over standard dual
and quad leaded packages. The leadframe die pad is exposed at the bottom of the package
and should be soldered to a properly designed thermal pad on the printed circuit board (PCB).
This provides a more direct heat-sink path from the die to the board,
and the addition of thermal
vias from the thermal pad to an internal ground plane will dramatically increase power
dissipation. Soldering the exposed pad also significantly improves board-level reliability during
temperature cycling, key push, package shear, and similar board-level tests.