Socorro !! ja usei mais de 5000 stm32f102 .no VCC 3,3V lm1117 ajustavel ST . foi montado fixo de 3,3v , com os resistores de 220r da saida para o ajuste e 360r . dopout de 1V alimentou o STM32 com 4V. o que acontecera ? Socorro !! 240 em operação.

[Peter BENSCH]

Welcome, @HFilh.2​, to the community!

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Help !!! i have used more than 5000 stm32f102 .at VCC 3.3V lm1117 adjustable ST . fixed 3.3v was mounted , with 220r resistors from output to adjust and 360r . 1V dopout fed the STM32 with 4V. what will happen ? Help !! 240 in operation.

As far as I understand, an LD1117 (LM1117 is not from ST) supplies an STM32F102. Instead of a 220ohm resistor in the feedback, 360ohm has now been fitted, which leads to a higher output voltage of 4V, right?

Well, in the data sheet of the STM32F102, a maximum value for the supply voltage of 4.0V is given in the Absolute Maximum Ratings. If this is exceeded, STMicroelectronics can no longer guarantee that the STM32 will survive.

So if it really is only 4.0V voltage that was inadvertently applied because of the wrong resistor, you don't need to worry: just change the resistor and the problem would be solved.

However, I doubt that it is only 4V applied at 360ohm, because you can use the equation for the output voltage, where Vref and the second voltage divider resistor R1 are considered constant and then Voutb = (R2b/R2a)(Vouta-Vref)+Vref, which with R2a=220 and R2b=360, however, results in an output voltage of 4.6V --> out of warranty.

It may be that the STM32F102s have even survived this and also seem to continue to function without problems, but medium-term or long-term consequential damage cannot be ruled out due to migration effects on the chip.

This may be acceptable for hobbyist purposes, but no longer for professional purposes, so that the STM32s must then be considered destroyed.

Exceptionally, I also have the text translated by an online translator, so please overlook grammatical errors:

Como excepção, também tenho o texto traduzido pelo tradutor em linha, por isso, por favor, ignorem os erros gramaticais:

Tanto quanto sei, um LD1117 (LM1117 não é de ST) fornece um STM32F102. Em vez de uma resistência de 220ohm no feedback, foi agora instalado 360ohm, o que leva a uma tensão de saída mais elevada de 4V, certo?

Bem, na folha de dados do STM32F102, um valor máximo para a tensão de alimentação de 4,0V é especificado nas Classificações Máximas Absolutas. Se isto for excedido, a STMicroelectronics já não pode garantir que a STM32 sobreviva.

Assim, se na realidade é apenas 4,0V de tensão que foi acidentalmente aplicada por causa da resistência errada, não precisa de se preocupar: basta mudar a resistência e o problema será resolvido.

No entanto, duvido que seja apenas 4V aplicado a 360ohm, porque pode usar a equação para a tensão de saída, onde Vref e a segunda resistência divisora de tensão R1 são consideradas constantes e depois Voutb = (R2b/R2a)(Vouta-Vref)+Vref, que com R2a=220 e R2b=360, resulta, no entanto, numa tensão de saída de 4.6V --> fora de garantia.

Pode ser que os STM32F102 tenham mesmo sobrevivido a isto e também pareçam continuar a funcionar sem problemas, mas não se podem excluir danos consequentes a médio ou longo prazo devido a efeitos de migração no chip.

Isto pode ser aceitável para fins de hobby, mas já não para fins profissionais, pelo que os STM32s devem então ser considerados destruídos.

Isso responde à sua pergunta?

Regards

/Peter

[HFilh.2]

Good morning Mr. Peter,thank you very much for the answer, your calculations are correct, at first I thought like you, the lm1117 input is powered by a flaybakde regulated 5V output source. with the dropout of the regulator it is 1V so it always applied 4V it did not go beyond this. But in the STM32f102 manual it doesn't say exactly what can happen.

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[Peter BENSCH · Accepted solution]

The dropout voltage of an LD1117 is specified as max. 1.1V at 100mA, but an STM32F102 has considerably lower current consumption, so the dropout voltage might be significantly lower. This in turn increases the output voltage in your case.

In addition, in your case a flyback is working, whose switching frequency appears as a ripple at the output. This ripple also increases the input voltage, which exacerbates the problem.

By the way: the Absolute Maximum Ratings are the values that must not be exceeded under any circumstances, because otherwise no guarantee can be given for the parts.

It therefore no longer matters what could happen then. As already mentioned, for professional use the STM32s must be regarded as pre-damaged and disposed of or replaced by new ones.

I am very sorry not to be able to give a more pleasant answer.

If the problem is solved, please mark this thread as answered by selecting Select as best, as also explained here. This will help other users find that answer faster.

Regards

/Peter

[HFilh.2]

Mr. Peter I fully agree with Mr. , you are completely right. This position of changing the processor is what I believe. It arrived from 4.00 to 4.15V the problem is that we didn't notice because the boards worked well. the regulator is on a processor board next to the STM32 and feeds only to it. A test routine was missing to verify this voltage. Several were delivered to customers and are distributed throughout Latin America. The problem I have is that the product is in a high voltage risk area where only trained people can enter. I will draw up a plan for the exchange. Thank you very much have a nice day and have a nice weekend.

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