Calculate caps for LSE crystal oscillator

[nadeemtamuk191]

hi,

i am using a ECS-.327-9-34QCS-TR with a 1.5pF caps on a STM32H743BIT6.

I want to know the exact method to calculate the right value for the oscillator caps.

because my RTC is off by 5mSec.

[nadeemtamuk191]

GOING FROM 1.5PF TO 6PF  did not make much of a difference tbh.

may be there should be done some thing in the cube MX

fyi i did use High driver level

[nadeemtamuk191 · Accepted solution]

i used a 4pf for each load caps to avoid ringing and adjusted in the STM cube to get the proper value

4PF

my oscillator can handle 9PF, so 5pf is the IO cap according to the datasheet in the MCU 

9-5 = 4

[TDJ]

Just read AN2867 - Oscillator design guide for STM8AF/AL/S, STM32 MCUs and MPUs.
Use only oscillators listed in AN2867, but even then you may experience problems.
External capacitors generally should be 1/2 of the specified crystal capacitance since two capacitors are required.