32G431 power supply problem

[JJeba.1]

Hello

I am a total beginner in the STM world. Two months ago I migrated from arduino to STM and this forum hase been a lot of help.

But for this problem I cannot find a rational explanation.

Anyway I am making a custom board with the 32G431KB MCU and i have a problem that seems power supply related.

I use a ST-Link colne and so far I managed to program a few MCUs but this one is causing me problems.

Anyway I have a custom board with Lm1117-3.3v refulator and 100nF decoupling caps close to the MCU pins and a 22uF at the output of the regulator.

If I power the MCU with 3.3V the CubeIDE and programmed does not recognize the device but if I put 3.3V in the input of the LM1117-3.3 the output voltage drops to about 2.4V I can program the MCU and debugging works as expected.

I have removed the regulator from the board and tried powering with 3.3V and it does not work. But if I put a diode in series with the 3.3V to bring down the voltage to 2.6V it works again.

I ran out of ideas what could be wrong.

If I program the MCU and then run it with 3.3V everything is ok. I just can't debug and program at 3.3V

​I hope i explained good enough.

Thank you

[moatjon]

Hi JJeba.1,

It's very hard to find the root of the problem you describe without having a look at the circuitry. Can you post your schematics and PCB?

[JJeba.1]

I would love to but my USB key that had the only copy is broken. Maybe my friend that made the board has it. It's nothing special. all VDDs and VSS are connected together and I put 100nF decoupling close to all the VDD pins. There are four leds connected to the board and four DS18B20 sensors with 2k2 pullups ( I removed them to test if there was the problem). And I have an ISL3179EIBZ (RS485 transceiver) connected to UART1 (PA9 and PA10). And that is it. Oh and I have a 24MHz crystal ( i changed to the internal 16MHz and it is the same).

BOOT0 (PB8) is connected to GND via 4k7 resistor. and NRST is connected to 3.3V via 4k7

[TDK]

It sounds like there is a hardware power issue somewhere. It doesn't really make sense that you would be able to program the chip at 2.6V, but not at 3.3V. That doesn't line up with how the STM32 functions.

[Piranha]

> NRST is connected to 3.3V via 4k7

Why? And I don't see capacitor mentioned... Have you read AN5093? Take a look on figures 3 and 8 regarding the NRST pin.

[JJeba.1]

No I dont have a capacitor on the NRST pin.. I will read the docs

[JJeba.1]

No luck guys. I'm gonna buy the NUCLEO-G431.

Thank you