I have a customer currently using LM2574MX-5.0/NOPB in 5V buck application. The data sheet says that for the SOIC version of the chip pins 1, 2, 7, 8, 9, 11, 13, and 14 are no connects but must be soldered to the PCB for best heat transfer.
I have two questions. First, can these pins be tied together and tied to the pcb as a group? Second, is there a defined size of pad we should use?