we are facing after migrating our design from STM32F405ZGT7 to STM32H743ZI.
We have an automotive application where a horn load creates significant EMI transients. With our previous design using STM32F405ZGT7, the system was stable and did not experience any MCU freezing or malfunction during horn activation.
However, after migrating to STM32H743ZI — while keeping the PCB layout, grounding strategy, power architecture, filtering components, and external circuitry identical — we began experiencing intermittent MCU freezing during horn actuation.
After extensive debugging and hardware validation, we observed the following:
The issue only occurs when ST-Link is connected.
When ST-Link is disconnected, the system behaves significantly more reliably.
The noise appears to be injected through the ST-Link interface path.
The horn generates high transient noise despite having local snubbers and filtering.
We have already implemented:
RC snubber across the horn load
EMI input filtering near MCU supply
Proper decoupling near all VDD pins
Ground plane continuity and star grounding where applicable
This behavior was not observed with STM32F405ZG under identical conditions.
We would like clarification on the following points:
Are there any known differences in debug interface robustness between STM32F405ZGT7 and STM32H743ZI?
Is the STM32H7 debug interface more sensitive to ground bounce or transient noise?
Are there recommended protection or isolation methods for ST-Link in high EMI automotive environments?
Is there any application note addressing EMI robustness of SWD/JTAG on STM32H7 series?
We suspect that higher core frequency, different internal architecture, or debug interface implementation in STM32H743ZI may be contributing to this sensitivity.
