STM32H7 HSE Amplitude

[Kilian Nötzold]

Hello I have a custom board with a STM32H753ZIT and I’m wondering about the amplitude of the HSE crystal. It is only 300mV (see the attached Image). It seems to wok but is this normal?

The crystal requires a load capacity of 20pF per datasheet, the caps on the board are 27p so this should be OK. (27pF/2+5..10pF)

[waclawek.jan]

Which pin, HSE output or input?

The crystal oscillator is basically an analog circuit, and also a low power one. It may quite well work at this level, and also you may be loading it by your oscilloscope probe, lowering the amplitude further.

JW

[Kilian Nötzold]

Thank you Jan for looking into.

UI read 300mV on pin 23 RCC_OSC_IN , 220mV on pin 24 RCC_OSC_OUT

It is a 10Meg probe with 15pF. I also tried to take capacity into account but without significant difference.

We are using the same type of crystal for the Phy and there is around 750mV.

[waclawek.jan]

If in doubts whether you are in a safe area, try to review AN2867.

JW

[PC1]

I know this has been a few years since active, but Killian did you resolve it? If so what did you do and/or what was the issue?

Thanks, PC1