STM32H745ZIT3 VCAP voltage issue

[neven]

Hello, I am in the process of bringing up a custom board integrating an STM32H745ZIT3. The chip is running with VDD at 1.8V and we plan to use LDO only mode for supplying the core. We have assembled our power delivery and MCU on the board, but we are having trouble when powering the board. We see that VCAP reached 1V briefly (for about 4 ms) before seemingly shutting off. The chip is unresponsive to flashing as well. The scope trace below shows VCAP (green) and the NRST signal (yellow).

Below is the relevant part of our schematic. 

We are unsure if we are encountering an issue with our design or if we have an assembly issue causing our board to be non-functional. Please let us know if we can provide any more information to clarify our situation!

[Michal Dudka]

If you've already uploaded a program there, then LDO is probably turned off. See http://www.efton.sk/STM32/gotcha/g201.html

[mƎALLEm]

Hello ​@Michal Dudka and welcome to the ST community,

What power mode you’ve set in the software? it should be set to LDO nothing else.

If you are using CubeMx, this is what you should set as config:

If you are using directly the HAL you must set the define in your project config: USE_PWR_LDO_SUPPLY

Otherwise you’ve locked you MCU and you need to unlock it by referring to these articles: