According to the datasheet of LP8864, If use the external BST SYNC input, the RBST_SET resistor should be chosen the closest boost frequency options with the external frequency. I wonder why there are such restrictions and what the consequences will be if this condition is not met. The EVM can also work normal when I use the external BST SYNC input of 200kHz with the 3.92kΩ RBST_SET.
Another question is that can the spread spectrum function reduce ripple?