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Topic: Long term stability of internal RC oscillator (Read 3905 times) previous topic - next topic

Smajdalf

That they have opposite response to temperature changes is ... interesting!
Itbis not so surprising: the typical characteristics graphs show this behavior. It is also true for Vcc. With increasing Vcc WDT frequency decreases while main oscillator frequency increases.

Jiggy-Ninja

So the main osillator varies over a range of about 100/18000?  About 0.5%?  That's not too bad.
That they have opposite response to temperature changes is ... interesting!

They have opposing response to voltage variation as well. The watchdog oscillator decreases in frequency with increases in temperature or supply voltage. The 8 MHz oscillator increases in frequency with supply voltage and temperature increases.

MrMark

Sadly it depends on temperature so much it is possible to determine temperature variations between night and day indoors hidden in my table drawer and so it is not possible to use it to some good time keeping without callibration to temperature.
This Application Note suggests the internal temperature sensor sensitivity is about 1 LSB/degree C.  Your figure has variation over about 8 LSBs. 

Just to get a feel for the oscillator variation over temperature, does about 8 C variation over the duration of the test seem about right?

Smajdalf

Just to get a feel for the oscillator variation over temperature, does about 8 C variation over the duration of the test seem about right?
Didn't think about this. I don't remember weather in the two weeks. But variation between noon of sunny summer day and midnight of a rainy day may be easily 8°C. We have windows to south and so weather has relatively large impact.

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