Issue in powering STM32H755ZIT6 based board

[sudarshanHebbar]

I am experiencing issues powering the STM32H755ZIT6 MCU on our custom board. The schematic has been derived from the NUCLEO-H755ZI-Q development board reference design, and we have verified that there are no apparent design or assembly errors. However, the MCU fails to power up as expected.

All VDD pins are connected to an external 3.3 V supply (VDD_MCU). For the power supply configuration, we selected the default internal SMPS-only configuration, identical to the NUCLEO-H755ZI-Q board, as detailed below:

VDD_MCU is connected to VDDSD (pin 16).
VLXSD is connected through a 2.2 µH inductor to the VDDLDO pins (70, 105, 143) and the VCAP pins (68, 103, 140).
In CubeIDE, PWR_DIRECT_SMPS_SUPPLY is selected under RCC > Power Parameters > Supply Source.
Power Regulator Voltage Scale 3 is selected under RCC > Power Parameters > Power Regulator Voltage Source.

When powered from the external 3.3 V source, both VDD_MCU and VDDSD are at 3.3 V; however, there is no voltage present at VLXSD (SMPS output), and consequently no voltage at the VCAP pins.

When the board is powered via ST-Link, VDD_MCU and VDDSD measure approximately 2 V, and the SMPS produces an output of around 1 V, allowing the cores to power up. However, the peripherals do not function correctly, as they require a 3 V supply.

Please find the attached screenshots of the schematics for reference. Appreciate your guidance in identifying and resolving this issue.

Note: The BOOT0 pin (pin 135) pull-down resistor, which is missing on the PCB, has been connected manually during these tests.

[Gyessine]

Hello @sudarshanHebbar 
Just for verification:
You stated that you are using the second configuration, which requires 100 nF capacitors near VCAP.

However, your schematic shows that you are using 2.2 μF capacitors, which are the specifications of the third configuration (SMPS and LDO cascaded).

Other than that, I do not see a major issue for now. I will contact you if I notice something else.
Your schematic is very close to the Nucleo product schematic.
Can you double-check your wiring for short circuits or anything that can cause this voltage drop
BR
Gyessine

[sudarshanHebbar]

Thank you for pointing that out. I will replace those with 100nF and come back with the update.