Unstable voltage supply to STM32U

[KKots.1]

Hello all, 

I have designed a board for sensing purposes and I am using the following ST components: STM32U575ZIT6Q. 

I am supplying this component with 3V3, which I get form a 5V/3V3 LDO. Between the output of the LDO and the supplying rail to the STM I have placed a shunt/jumper. 

Whenever the this jumper is not shorted/ is open, so it is not supplying the STM, the voltage reading I measure seems perfectly fine. However, once I short it and allow the STM to be supplied by this 3V3 rail, I notice the behaviour depicted in the pictures below. 

It seems like some kind of protection is being triggered, however so far I have not been able to find what the issue is.  At the same time, I notice that the STM is getting quite hot. 

I would really appreciate any suggestions or recommendations. 

Best regards, 

Kosta Kotsis

[TDK]

A few possibilities:

• Power pins un- or mis-connected.
• Workmanship issue such as solder bridges between VDD/VSS pins.
• Incorrect part rotation.
• Schematic error.
• Board manufacturing error.

Include your schematic if you can, and/or high resolution images of the board.

[KKots.1]

Hello, 

I just included an image of my schematic.                                                                                                                     

I have checked the orientation and pins of the component and those seem to be fine. 

So I am currently suspecting that there is something else that I am missing. 

 

Best regards, 

Kosta Kotsis

[TDK]

VDD11 shouldn't be connected to 3.3V. It should only have a capacitor to ground, on both pins, if you're not using SMPS.

Per the hardware layout guide:

https://www.st.com/resource/en/application_note/an5373-getting-started-with-stm32u5-mcu-hardware-development-stmicroelectronics.pdf

 

[TDK]

Might not be killing you here, but VDDIO2 is required per the datasheet, and since you're using pins supplied by that rail.

[KKots.1]

Hello, 

Thank you for the suggestions. I will try to do some repairs on the PCB based on your feedback and see if that will work. Hopefully I will give an update soon. 

Best regards,

Kosta

[KKots.1]

An update: 

I have desoldered the pins and have connected them based on the recommendations above. The VDD pins are now reading 1.1V and the issue described above is solved. 

However I am now unable to comunicate with the STM chip. Could the mistake described above have broken the chip? 

Thank you in advance for any recommendations. 

Best regards,

Kosta Kotsis

[TDK]

> However I am now unable to comunicate with the STM chip. Could the mistake described above have broken the chip? 

It could have, yes, but in my experience it generally doesn't.

Are VDD pins measuring 3.3V and VDD11 pins 1.1V?

And VDDIO2 pins connected to VDD?

Quite a bit of rework there.

JTAG seems to have more issues than the standard SWD debug connection.