The LT8490 makes reference to the LT8705 data sheet for the switching configurations
The LT8705 says:
"Figure 4 shows the regions of operation for the LT8705 as a function of VOUT -VIN or switch duty cycle DC ... When VIN is significantly higher than VOUT, the part will run in the buck region"
Can someone define the numerical minimum difference in output voltage and input voltage where the chip would be in buck mode please.
You can find this in page 16 of LT8705 datasheet. Use the two equations there.
It depends on the switching frequency. Use 2nd equation DC(ABSMIN,M2,BUCK) then the 1st equation. On a 48Vout application running at 350kHz, the operation will be in buck mode when Vin goes to about 52.8V and higher.