Can’t connect to target MCU on custom board based on STDES-WL5U4SBB (MB1720)

rohithinthingstech · ‎2025-07-15

Hi ST Community,

I have developed a custom board based on the MB1720 HighBand HighPower A01 reference schematic (STM32WL series). On my custom board, I’m unable to debug the MCU — my debugger can’t connect to the target at all.

I’ve double-checked the power rails (VDDRF, VDDPA, VDDRF1V55) and they seem fine.
However, I’m not sure if I made any mistakes when replicating the debug interface or SMPS configuration.

Could you please help me check:
1.Is the debug circuit (SWD/JTAG lines, NRST, BOOT0) correctly implemented?
2.Are the power supply and SMPS sections connected properly for the STM32WL to boot and allow debugging?
3.Any common mistakes that could cause the debugger not to detect the target MCU?

I’ve attached my schematic

Andrew Neil · ‎2025-07-15

@rohithinthingstech wrote:
my debugger can’t connect to the target at all.

What debugger?

What, exactly, happens when you try to connect? Show logs, screenshots, etc ...

How to solve connection errors when connecting and programming the STM32 target board.

How to solve debugger connection issues

How are you connecting GND and VDD to the debugger?

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.