STM32F072C8T6TR VDDIO2 power

[HVan .3]

Hello,

I have a board that use STM32F072C8T6TR reference.

After severel weeks of normal use, the STM32 on some boards are not responding anymore. I tried to access the STM32 with STlink Probe, ore by using internal Bootlaoder, without success. After investigations, I can see that the NRST pin (which is internally pulled up, and not connected to any other component on my board) never goes high, and thus I suspect that the MCU is dead.

The STM32 only use some GPIOs for SPI communication with components that share the same VDD Power supply.

The only idea I have, is that the VDDDIO2 that power the USB PHY and some GPIOs is only powered when a USB cable is connected to my board. I understood in the datasheet that the VDD and VDDIO2 domais are completly independant, and thus the VDDIO2 can be shut off even if the STM32 is running.

Is it correct ? If not, could it explain the behaviour I have ?

Thanks,

[Uwe Bonnes · Accepted solution]

Read the datasheet again: "The VDDIO2 voltage level is completely independent from VDD

or VDDA, but it must not be provided without a valid supply on VDD."

[HVan .3]

Hi Uwe,

Thansk for your answer. I agree with you, and our design respect the datasheet :

• the VDD+VDDA are automatically provided when the board is powered up
• the VDDIO2 is provided when the a USB cable is plugged, but only when the VDD is already present. If the VDD is not provided, the VDDIO2 is shut on my board (using load switch).

Thus, the VDDIO2 cannot be provided without a correct VDD, in accordance to the datasheet.

[Uwe Bonnes]

If the source supplying VDDIO2 is capable, consider a Zener of about 3 V between that source and the main source. If the difference gets higher than 3 Volt, main VDD is pull up, so the 4 Volt limit will not be reached.