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XMC™ Forum Discussions

Qu19_4750531
Level 2
Level 2
Hello,

Is there any information available on XMC4700 internal RTC stability/drift with time and temperature ?

I am trying to analyze stability of XMC4700 internal RTC. In order to do this testing, i have connected ST external RTC and internal XMC4700 RTC to same crystal source of 32.768 kHz. I
initialize both internal and external RTC 's to 0. Then my application accept PC time from the user and configure both RTC's as per PC time.
When i ran both RTC's for 45 mins, i could see internal XMC RTC was 16-21 secs ahead of PC time. When i ran this set up for 4 hrs, XMC rtc was 1 min 43 sec ahead
of PC time and external RTC time. Both the test cases were performed at room temperature.

Has anyone seen similar behavior of drifting with time with internal RTC ?

While configuring PC time in internal RTC i simply update register by calling XMC_RTC_SetTime function.
Is there any specific sequence do i need to follow ?

Any feedback is appreciated.

Thanks

Query1920
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1 Reply
User19222
Level 1
Level 1
Hello Query1920,
Internal Oscillators are never quite precise. They all work on the principle of an RC-Oscillator.
This also means, that the uncertainty of manufacturing the on chip resistor and capacitor is reflected as an uncertainty in timing, as the time constant (tau = RC). Taking (103 seconds / (4*3600 seconds)) = 0.715%.
This means that the on chip resistor and the capacitor probably have a precision of up to 1%. That is exactly the reason, why crystal oscillators are used. They have a precision in the 5ppm - 100ppm range.
Best Regards,
JJLK
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