Good day. I am working on a 32-pin STM32U083KCU6. This requires the use of LSE 32.768kHz crystal. I referred to AN2867 as the oscillator design guideline. The LSE has the following specs: Shunt capacitance - 1.15pF, ESR - 70k, Load capacitance - 7pF. Calculated crystal gm is less than the STM32 Gmcrit so I think this crystal is ok to use. My concern is the determination of Rext value as the measurement of the current through the crystal is not an easy measurement. To set baseline in the Rext value, I used the evaluation board NUCLEO-U083RC as reference since it uses a similar STM32U083RCT6. Looking at the evaluation board schematics, I see that the Rext R34 and R35 are both set to 0R. The LSE used in the evaluation board is NX2012SA-32.768KHZ-EXS00A-MU00527 which has a max level drive of 0.5uW. May I ask to what drive level is the MCU set to drive the crystal in the evaluation board? What is the power level the MCU drives the crystal considering the max level of drive of the LSE is 0.5uW? Appreciate your support on this topic. Thank you.
