Unable to flash or debug STM32L432KCU at 3.3v, but works at 2.2v?

[cegar]

Hello,

I have an STM32L432KCU chip that's on a custom board. I have exposed SWD pins for debugging and flashing. Currently I'm only able to flash and debug the chip if I supply the STM with 2.2v from my external power supply. If I run the STM at the standard 3.3v, I get the "No STM3 target found" message when using CubeIDE, plus running CubeProgrammer, I also cannot connect to the STM to read the flash contents but can at 2.2v. These are fresh chips with no previous firmware flashed onto them, so I don't believe they should be in low power mode. Even if they happen to be in low power mode from the factory, I flash them at 2.2v with a default program to ensure they aren't running in a low power mode.

After flashing the chip at 2.2v, I can supply the normal 3.3v and the chip runs just fine. However, for me to debug or flash new firmware, I can only get it to run at 2.2v. Any ideas?

[STOne-32 · Accepted solution]

Hello @cegar ,

It might be an issue on the Debug Probe , I assume an ST-link ? If possible to have picture and also how is wired to the target MCU  : pull-up or pull-down in SWD or JTAG pins + NRST

Hope it helps ,

STOne-32

[cegar]

Hello,

Sorry I forgot to post which debug probes I'm using.

I've tried using the official 20-pin ST-LINK/V2 and those cheap knockoff 10-pin USB ST-LINK/V2 debug probes, but both have the same result at only detecting the STM when it runs at 2.2v.

Sorry I don't have the schematic, but we are basically copying what the Nucleo L432KC does things with some exceptions:

• SWDIO and SWCLK exposed through standard header (no pull-up/pull-down)
• BOOT0 tied to GND with 10k resistor
• NRST tied to VDD with 10k resistor

[cegar]

Ended up adding 15kOhm pull-up resistors on my SWDIO and SWCLK lines and I was able to debug at the 3.3v.

I've never encountered this issue on other custom STM boards I've worked with so not sure why I had to add pull-up resistors this time.