LSE RTC crystal drift
Posted: Tue Feb 07, 2023 6:27 pm
Hi all
I made a custom board based on STM32L052C8T6 with a 32.768Khz crystal (ABS05-32.768kHz-T) and 2x15pF caps.
I uploaded simpleRTCAlarm example that fires an alarm every 60 second. If i use the LSI every alarm fires around 58 seconds (measured with my stopwatch). But if i use the LSE every alarm takes around 75 seconds, that's a 15 seconds drift.
ABS05-32.768kHz-T has 12.5pF of load capacitance, considering 5pF for stray capacitance i calculated 15pF for the crystal caps.
Is this configuration ok? Could be a defective crystal? Any other idea?
Thanks
I made a custom board based on STM32L052C8T6 with a 32.768Khz crystal (ABS05-32.768kHz-T) and 2x15pF caps.
I uploaded simpleRTCAlarm example that fires an alarm every 60 second. If i use the LSI every alarm fires around 58 seconds (measured with my stopwatch). But if i use the LSE every alarm takes around 75 seconds, that's a 15 seconds drift.
ABS05-32.768kHz-T has 12.5pF of load capacitance, considering 5pF for stray capacitance i calculated 15pF for the crystal caps.
Is this configuration ok? Could be a defective crystal? Any other idea?
Thanks