According ADM1278 datasheet, If the ADM1278-2 model is used but the SPI pins are not required, tie the SPI input pins (SPI_SS, MCLK) to VCAP and the SPI output pin (MDAT) can be left floating or tied to GND.
SPI_SS > pin 9
MCLK > pin 10
MDAT > pin 11
But Is it necessary to tie pin9 & pin10 to VCAP? Can I leave both of them floating?
Thanks very much!!