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STM32H7 HSE Amplitude

Kilian Nötzold
Associate III

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)

4 REPLIES 4

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
Associate III

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.

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

JW

PC1
Associate II

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