After the overall power tree was roughly settled, I started with the MCU power supply. I want the MCU to handle low-level monitoring and management for the whole board.

I am not using a PMIC for power sequencing. The board has many chips that need different voltages, and some rails are shared. A PMIC would take a lot of board area, and it is hard to find one that matches everything. So I merged rails at the same voltage and use load switches to control power-up.

Without a PMIC, something still has to control the sequence. I gave that job to the MCU. One reason is that I do not need a complex bring-up path for the STM32 itself: with USB disabled and VREF on the internal reference, it can boot from a single 3.3 V rail. Another reason is that USB is not used on the MCU in my design (USB goes to the V851S). I only need to monitor each rail coming up, so ultra-high precision is not required.

Current progress: the basic MCU power-on circuit is drawn. Power sequencing control is not in the schematic yet.

MCU power schematic: