STM32H745BIT6 MCU Failure Investigation Request – NRST Held Low on Multiple Boards
Hi STMicroelectronics Team,
We are observing MCU failures on multiple IO Controller boards and request your support for detailed failure analysis.
On the affected board (BIO-14), the MCU remains continuously under reset and STM32CubeProgrammer reports "DEV_TARGET_HELD_UNDER_RESET". We are also unable to communicate through DEBUG_UART.
Key observations:
- NRST voltage with power ON: approximately 0 V
- NRST to GND resistance: approximately 1.2 Ω
- VDD_MCU to GND resistance: approximately 152–155 Ω
- VDD_MCU: 3.3 V when powered ON
- VCAP to GND resistance: approximately 2.67 kΩ
- BOOT/RST recovery attempts and STM32CubeProgrammer Under Reset/Hardware Reset connections at 1000 kHz and 400 kHz were unsuccessful
Similar MCU failures have been observed on approximately three boards. We would like to send the failed MCU(s) to STMicroelectronics for failure analysis.
Please help determine the failure mechanism and root cause, and advise whether the absence of an external pull-up resistor on the NRST line or any other design/operating condition could be contributing to the failures. We would also appreciate your recommendations for corrective and preventive actions to avoid recurrence.
Given the occurrence across multiple boards, we request your priority support on this investigation and guidance on the process for submitting the failed devices for analysis.