TPS53676: Connection of VIN_CSNIN, CSPIN if current sensing not used

Hi. I'd like to check which rail is the "input voltage" mentioned in the datasheet Table 5-2 Pin Functions (page 5) referring to? Is it VCC (3.3V supply to TPS53676) or the buck's input rail (the rail connected to buck high-side MOSFET)?

Thanks,

YokeMun