MCU doesn't start after power cycle; Reset works OK

[KaushikChavda]

Dear Team ST,

We are using the STM32 MCU (Part No. STM32F407VET6) on our custom board, and we are currently facing an issue related to the reset function.

During board power-on or after program loading, the MCU appears to enter a hold or non-responsive state. This issue occurs every time the board is powered OFF and then powered ON. However, when the hardware reset button is pressed, the MCU starts functioning as expected.

We kindly request your support in identifying the root cause of this issue. Please advise if any modifications are required on the firmware or hardware side to resolve this behaviour.

We look forward to your guidance.

Regards,

Kaushik

@Shubham Prakashpant BOHARAPI

[mfgkw]

Hi Kaushik,

your problem might be related to the power supply while starting.

But it is hard to understand your problem without knowing your custom board.

You will have to provide more information, e.g. the board schematics.

BR Klaus

[KaushikChavda]

Thanks Klaus

Here i am sending the power supply and MCU section schematic for your reference.

Please suggest further modification.

Regards,

Kaushik

[mansi]

Hi Kaushik,
I've encountered this problem with various CPUs. The solution we found is to use a reset monitor like the MAX 803 series or similar. I've attached the datasheet.

It's usually a problem with the time it takes for the Vdd to rise in relation to the reset signal

[KaushikChavda]

Thanks.

As of now we can not revised Our hardware board. Please suggest, Any modification required on POR, coding side, any changes on .IOC file.

[MGogr.1]

We have used similar controller on your custom board but never have encountered such problem.

BOOT0 and BOOT1 pin we have grounded using 22k resistor. And NRST pin with RESET pin of Debugger.

[mfgkw]

I am afraid it is a HW issue and will not be solved on SW side...

[TDK]

VCAP capacitors should be 2.2 uF, not 0.1 uF.

VDDA should be tied directly to VDD, not through a resistor.

[KaushikChavda]

Thanks, I will implement suggested things, and get back to you soon.

[Ozone]

Yes, I think so as well.

The power supply rails don't come up correctly, due to the design of the supply part.
Not enough buffer caps, inapproriate values or types, or inapproriate placement (not near the MCU).

When one presses the reset button several seconds later, the supply is stable, and everything works fine. This is to be expected.

ST has specific recommendations for hardware design, and the F407 is not a low-power MCU.