No STM32 Target Found - Custom board

[TEsli.1]

Hi guys,

I recently made a design based on nucleo wb55 dongle using STM32WB55CGU (48-UFQFN), but I cannot connect to it using SWD.

I believe it is not a schematic problem, so I am a bit stuck for debugging the situation. I soldered it using hot air station (< 250/260 deg celsius). The joints look okay, but I am not an expert on soldering QFN. So, my main guess is that I broke it while soldering.

• Is it really feasible to solder it using hot air station ? or a reflow oven is a must ?
• I compared the voltage on the dongle with my custom board, and the difference I find is on pin VLXSMPS, and VFBSMPS. It is 3.3V on dongle, but 0V on mine. What could be the reason ?
  • It is not shorted to GND.
  • I tried to short it to VDD, but it didnt help
  • 
  •  
• NRST is at 3.24V
• I use the ST-Link V2 to program it, same as what I use on the dongle

Thank you very much for your time

SWD

MCU Schematics

VDD 

External Clocks

[MattKefford]

The NRST pin has a built in 40k pull-up so are you sure you need the external one? Could be preventing the debugger from resetting the device?

[MattKefford]

Do you have a screenshot/snip of the SWD connector? Are there any other components added like diodes or just connections straight to the MCU?

[MattKefford]

If you are suspicious of the SMPS you could try modding the circuit to the LDO configuration just as a test:

[TEsli.1]

Thank you for your reply.

I didn't know about the internal one actually, I can try to take it out to test. I took the schema from https://www.st.com/content/ccc/resource/technical/layouts_and_diagrams/schematic_pack/group0/6f/4a/27/3b/7d/c4/43/f8/mb1293_schematics/files/MB1293-WB55CGU-C02_schematic.pdf/jcr:content/translations/en.MB1293-WB55CGU-C02_schematic.pdf

The connections for SWD are straight to MCU. I have added a screenshot in the original post.

[TEsli.1]

I will try the LDO

[TEsli.1]

That's the same in LDO, but good point. Thank you

[TEsli.1]

Does it need the external clocks to be able to connect with SWD ?

[MattKefford]

It looks like you need a 32MHz external for the RF but the device has HSI16 and HSI48 built in so should be able to run using those. I made a custom board too and I can use it with or without external crystals. Saying that I haven't worked with one of these, mine is just an F0 board. Do you have the crystals fitted?

I suppose just keep probing with the multimeter. The ST Link should be happy as long as the Vdd pin is close to 3.3V and ground is 0V and the RST pin is above 2.3V.

Could try produce a few more boards, you said you're not so confident at hot air soldering so maybe it would take a few attempts?

[TEsli.1]

Yes, I also think the internal crystals should be enough for WB55. I probed everything on my board, and on the dongle ahah, kind of desperate.

The crystals are fitted indeed.

I will produce some more, and lets see ! Hopefully, I can get it running

Thank you very much for helping out. Thats very helpful