I am trying to choose a crystal for the STM32F7. The only problem being is that I cant find a component that respects the recommended values found in the following arm design guide. Even STM for it's STM32F779I-EVAL board does not respect the gain_margin.
If I have understood correctly there is one main rule governing the choice for a crystal so that the oscillator starts and reaches a stable phase.
gainmargin = gm / gmcrit
gm is the oscillator transconductance specified in the STM32F779 datasheet.
- Gm_crit_max = 0.001
gmcrit is computed from oscillation-loop passive components parameters.
- ESR is the equivalent series resistance
- C0 is the crystal shunt capacitance
- CL is the crystal nominal load capacitance.
- F is the crystal nominal oscillation frequency
The one used for the eval board is this one : NX3225HA
But I found gainmargin = 1.674730 when it's supposed to be >5
Does anyone know why?