STM32H503CBT6 NRST and VCAP Behavior – Severe Stability Issue
Hello,
I’m using the STM32H503CBT6 microcontroller in my project. At this stage, the firmware simply toggles a single LED. I’m using STM32CubeMX (code configurator) and compiling with STM32CubeIDE. The system is configured to run at 250 MHz using a 16 MHz HSE with the PLL, according to the recommendations in the documentation.
Hardware Configuration:
NRST pin is pulled up to 3.3V with a 4.7k resistor and has a 100nF capacitor to GND.
BOOT0 is pulled down to GND with a 10k resistor.
Both VCAP pins have 2.2µF ceramic capacitors.
All unused GPIOs are left in floating mode via CubeMX configuration.
VDD is supplied with a stable 3.3V.
Observed Issues:
The system enters a fault state randomly, between 10 seconds and 10 minutes after power-up.
In the fault state:
VDD remains at 3.3V.
NRST pin oscillates between ~0.5V and ~0.9V.
VCAP voltage drops to around 1V (where it should normally be ~1.36V).
Before entering the fault state, NRST sometimes fluctuates between 3.3V and 2V for a short while.
After the fault, the microcontroller becomes permanently non-functional. It starts drawing excessive current and does not recover.
So far, we’ve damaged around 20 STM32H503CBT6 chips across different PCBs.
Power has been supplied from different sources:
USB port of a computer,
Regulated lab power supply,
3.3V battery source.
The same issue occurs with all power setups.
Best regards.