Hi,
in order to disable Sleep mode (set SLPC bit) you need to program MTPNV cells, here address 0x74. If the device has been programmed previously, the factory presets may need to be restored before reprogramming can begin. Read chapter 7.11 Non-volatile SBC configuration of the device datasheet for more info.
If using SBC's SDK driver then there is a function to change factory preset value of non-volatile memory.

just set factories.control.slpc accordingly.
BR, Petr