2018-08-21 07:34 AM
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)
2018-08-21 11:56 AM
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
2018-08-22 12:47 AM
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.
2018-08-22 02:27 AM
If in doubts whether you are in a safe area, try to review AN2867.
JW
2022-02-07 09:12 AM
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