SPRADO8 March 2025 AM62L
VDD_RTC needs to ramp up before VDD_CORE and ramp down after VDD_CORE. A diode is used at the input of the discrete LDO used to generate VDD_RTC. Without the diode the VDD_RTC power rail can decay at the same time or before VDD_CORE when there is a uncontrolled power down, where the system power supply is turned off or disconnected from the board.
The VDD_RTC power domain does not draw much power, so the input capacitors on the VDD_RTC LDO hold the VDD_RTC rail valid for a long time when this is isolated from the input power supply with the diode.