Why I did not get a SWD conection from STLink-V2 to STM32L4Q5VGT6P

[CSeid.1]

Hi all,

I have an STM32L4Q5VGT6P (LQFP100) on my own board. The supply voltage is +3V3 without an external oscillator. Unfortunately, the STM32 CubeProgrammer does not connect to the MCU via SWD. Error message "No STM32 Target found" (Erata of the MCU says no connection via JTAG possible so I use SWD) The STLink-V2 has the latest firmware on it. What could that be? What are the minimum connections for this MCU to get started?

When I connect the STLink-V2 to my own board with an STM32L4Q5CGT6P (LGFP48), everything works fine, but I can't connect to the STM32L4Q5VGT6P.

I know there are two pins (VDD12) for an external SMPS. These are not wired by me. I can measure a voltage of 1.2V at the two pins.

According to my understanding, these two pins are not necessarily to be connected if you do not necessarily want to save power. I only bought the MCU's with the "P" because MCU's without the "P" aren't available for a long time.

Who has a hint?

Thanks in advance

Best regards

Christian

[gbm]

Make sure that all the GND and Vddxx pins are connected and 100 nF capacitors are present where they should be. Connect GND, SWDIO and SWCLK to ST-Link. Supply 3.3 V from an external source or from ST-Link (if you use Nucleo board ST-Link, note that there is no Vdd output in the SWD connector - use Vdd from Morpho vonnector).

[S.Ma]

Check the datasheet pinout table, especially the differences between both packages. Then check an ST board using the smps mcu to check what the different pins should be wired to. Force you chip at boot pin when reset goes high if the flash was preprogrammed to exclusr fw that reconfigure the pins or go clock stop mode which may cause a working swd to become unresponsive.

[CSeid.1]

Hello,

@gbm: All Vdd's and all Vss's are well connected with a 100nF capacitors (All Vdd & Vss pairs). Also the SWDIO and the SWCLK pins are properly connected. The only things I'm not sure are the two VDD12 pins.

@ .. : The Boot Pin is connected to GND with a 100k resistor. What do you mean with "Force you chip at boot pin when reset goes high if the flash was preprogrammed to exclusr fw that reconfigure the pins or go clock stop mode which may cause a working swd to become unresponsive."? The MCU's are new. I bought round about 70 pieces and the first three do nohting.

Thanks for the hint with the ST board. I'll be back later .

Regards

Christian