[SOLVED] STM32F4 custom board design problem

[Sİnel.1]

I designed a pcb with STM32F411RE and a couple of sensors. Before, and after mounting components on the PCB, I checked the Vcc and GND pins for short circuit and I did not see any problem. I am using SWD programming and I connected my ST-Link V2 to my board, successfully loaded the program. Everything was normal until a few minutes. Approximately 3-5 minutes after, MCU disconnected from PC and then I checked the Vcc and GND pins and observed short circuit. Interestingly, as time goes resistance between Vcc and GND pin increased by itself.

After that, I just mounted STM32F411RE, reset pin configuration and Vcap. I connected my board to PC and loaded the program successfully. However, after a while power pins shorted again. I just uploaded simple led blinking test program.

My board schematic is below. Please help me to find my mistake.

[Sİnel.1]

In second experiment, I mounted only STM32F411RE, reset pin configuration and Vcap on an empty PCB and same thing happened again, after a while power pins are shorted. I supplied 3.3V from ST-Link V2. In second experiment I did not use any voltage regulator. Is there anything wrong with the power supply of MCU?? I checked from datasheet and did not see anything wrong.

[Piranha]

That's not your problem, but still remove that R9. It's ridiculous how everyone copies that design from BluePill or something without even thinking.

Is the MCU damaged permanently or it still works later? Is AMS1117-3.3 damaged?

> In second experiment I did not use any voltage regulator.

What exactly do you mean by it?

[Sİnel.1]

After a couple of hours later, resistance between Vcc and GND increased to kohms. After that I connected the bord to PC via ST Link V2 debugger and loaded the led blink program, 1-2 minutes later connection was lost and I observed that Vcc and GND was shorted. I think that MCUs are not permanently damaged. However they are not working properly. I tried many times to load and erase the program for one MCU and finally it gave up ank sink more than 250mA.

In second experiment I did not mount, sensors, voltage regulators, opamp and other stuff. I just mounted STM32F411RE, Vcap(4.7uF) and reset pin configuration to reduce the suspicious component. I powered board 3.3V from ST Link V2. However same thing happened again.

I really did not understand the problem, I checked many times datasheet and F411RE-Nucleo board schematics.

[Sİnel.1]

Let me explain my last experiments on the PCB. For a second PCB I just mounted STM32F411RE, C5(Vcap), R9, C10, LED2, R11 and reset button. I did not solder any sensor, any voltage regulator etc. on second PCB. I used the power lines from ST-Link. I supplied only 3.3V to PCB. At the beginning I connected PCB via SWD to my computer and loaded simple LED blink program and everything works fine for a couple of minutes. After that I lost connection with PCB via ST-Link. I removed the power pins and see the short circuit.

LED2 is connected to the PC2 GPIO output pin of the MCU there is also a 220ohm resistor. I think that the problem is in the microcontroller. Because in second experiment there is nothing than STM32 on the board. However, you are right I2C line should not be pulled up to 5V. In addition to that in second experiment where only STM32 on the board. The current consumption was normal it was about 10-20mA. But after a while it shorted again.

[Sİnel.1]

Probably I solved the problem finally. I removed the LEDs and did not use flux while soldering the STM32F411 and changed the ST-Link. As a result, the board is working fine, however I did not mount all of the components. For now, I mounted STM32F411, HC-06 Bluetooth and reset circuitry and it works without any problem.

I think that the problem may be caused by the LEDs or the ports that connected LEDs or maybe the ST-Link that I used is damaged or there is something. In addition to that I doubt that maybe particles (dirt) in the flux may changed the conductivity of the flux.

Tomorrow, I am going to complete the board.

I will give a feedback from here. Thank you everybody for your contribution.:smiling_face_with_smiling_eyes:

[Sİnel.1]

Friends today I completed the board and it works good finally. I did not used any flux and did not mount LEDs and changed the programmer ST-Link. Thank you all again for your precious contribution. :smiling_face_with_smiling_eyes: