A large amount of power may be dissipated by the UCC21540-Q1 if the driving voltage is high, the load is heavy, or the switching frequency is high (refer to Section 10.2.2.6 for more details). Proper PCB layout can help dissipate heat from the device to the PCB and minimize junction to board thermal impedance (θJB).
Increasing the PCB copper connecting to VDDA, VDDB, VSSA and VSSB pins is recommended, with priority on maximizing the connection to VSSA and VSSB (see Figure 12-2 and Figure 12-3). However, high voltage PCB considerations mentioned above must be maintained.
If there are multiple layers in the system, it is also recommended to connect the VDDA, VDDB, VSSA and VSSB pins to internal ground or power planes through multiple vias of adequate size. Ensure that no traces or copper from different high-voltage planes overlap.