SNLS477B October 2014 – November 2018 DS90UB948-Q1
TI recommends that a consistent ground plane reference for the high-speed signals in the PCB design to provide the best image plane for signal traces running parallel to the plane. Connect the thermal pad of the device to this plane with vias.
At least 32 thermal vias are necessary from the device center DAP to the ground plane. They connect the device ground to the PCB ground plane, as well as conduct heat from the exposed pad of the package to the PCB ground plane. More information on the WQFN style package, including PCB design and manufacturing requirements, is provided in AN-1187 Leadless Leadframe Package (LLP) (SNLU165).