I am using the chip STM32F405 when developing a power converter. It is a buck converter.
When the input voltage is below 25V, I used the keil to debug the chip normally, and monitor the variables.
However, when the voltage is up to 40V or even more, I cannot debug any more.
The following is the SWD interface I designed
Debug hardware: STM32F0discovery working as stlink debuger
Debug target: STM32F405RGT
Debug interface: SWD
The power of the MCU is provided by standalone DC source of 3.3V.
The input voltage of the buck converter is provided by another DC source.
So, why I cannot debug the target when the input voltage is high? Is there any things I should paid attention to when designing the debug circuit in such high voltage application?