STM32F1 and STM32F4 external oscillator circuit shorted

[zexx86]

Posted on February 11, 2016 at 20:14

Hello,

I am facing quite strange issue when some of my boards are suffering very rarely from burned path in the MCU for external oscillator input.It happen with STM32F1 and also STM32F4 in the way, that I can measure less resistance in OSC_IN than in good MCUs.Nothing else than this pin is wrong.So this issue is happening from nothing. For example it works for 50 times and then next time the problem occur irreversible. There are even occasions when the problem is fixed on its own, but definitively the problem is just in the processor - after MCU replacement all is working again and the issue will not occur anymore.Is there any possible explanation for this?When the issue occur, MCU is still working, but only from internal oscillator.All boards are identical, but the issue happen only to maybe 1% from thousands.Thank you

[Danish1]

Posted on February 12, 2016 at 13:44

You do not say what you have connected to that external oscillator input.

If you just have a crystal (and the associated capacitors) between that pin and the external oscillator output, then I would not expect problems.But if you are driving that pin from an external oscillator (e.g. a TCXO) then you must be careful not overdrive the pin. Even if the TCXO is running from the same Vdd as the stm32, it might be that your pcb layout causes overshoot on either the rising or falling edge and these might kill the pin.Hope this helps,Danish

[zexx86]

Posted on February 12, 2016 at 14:13

Here is my scheme for the external oscillator.