Did I destroy my STM32F7? (SB12 removal)

[AKuts.1]

Dev board: Nucleo-F767ZI

Dear all,

as I wanted to have my own Vref+ for ADC conversions I removed solder bridge SB12 (coupling Vref+ with VDD) to input my own reference voltage (~3V) at Pin 6 CN7.

After removing the SB12 however the STM 32 device is not found anymore. I can still connect with the ST-Link and trying to reflash the device I get the following from CubeProgrammer:

  16:42:51 : STM32CubeProgrammer API v2.7.0
  16:42:57 : ST-LINK SN  : 066DFF343137524157233717
  16:42:57 : ST-LINK FW  : V2J37M27
  16:42:57 : Board       : NUCLEO-F767ZI
  16:42:57 : Voltage     : 3.24V
  16:42:57 : Error: No STM32 target found!

So did I physically destroyed something while removing the SMD or did I trigger some failure state that I can somehow reset? Any help is appreciated.

PS: Resoldering the bridge did not help. Surface looks clean, no unintended solder bridges visible.

PS2: LD7 blinks for a fraction of a second when attaching or detaching the ST-Link USB cable.

[TDK · Accepted solution]

SB12 connects VDD to VDDA (as well as VREF+). VDDA and VDD must always be connected per the datasheet.

 

If you put VDD=3.3 and VDDA=3.0, and redoing the bridge didn't fix it, I would guess it's dead. Although it still is reporting a board, so clearly it's still partially working.

Feel if the chip gets hot. If so, you probably blew out an internal protection diode.

[AKuts.1]

Thank you that is what I needed! Where did you get the datasheet from - it does not appear to be available from the ST Nucleo page.

I upped the CN 7 Pin 6 voltage to 3.3V and I was able to connect to the device again after some trial and error, however unable to run the code that did previously run. I erased the device with CubeProgrammer and resoldered SB12, but this time without the 0 Ohm SMD but just the solder and it works again now.

So as far as I see it is impossible to connect an independent Vref+ without affecting all the other curcuits that are connected to VDDA on the STM32767ZI.

[TDK]

> Where did you get the datasheet from

It's a schematic from the ST Nucleo page under CAD Resources:

https://www.st.com/en/evaluation-tools/nucleo-f767zi.html#cad-resources