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STM8L15x internal RC oscillator calibration

Question asked by Yevpator on Jun 23, 2011
Latest reply on Aug 16, 2011 by peng.james
Dear,

The allowed tolerance of oscillator frequency in my planned application is 1%. I'd like to use HSI and periodically to calibrate it. There is an application note describing the process + SW code. The method applied there is to measure some referenced frequency and to compare the measured frequency vs the known value. The frequency reference should be generated by an external crystal. The method is OK, but in this way external crystal is required( = money, PCB place). I thought about another approach. I'd like to calibrate the HSI oscillator with temperature sensor. The best thing would be to build any linear(or another) function - Freq (temperature) but the Datasheet does not have Freq vs Temperature characteristic ( just a range of -2 to +2 %), so if I want this approach I could try to find the function by myself in experiment, Or slightly another method is to build a look-up table, also in experiment.
In the mentioned App. note I found a brief notice regarding this method, but I have a little doubt perhaps I'm missing something and I'm not paying attention to a potential problem that might exists with this approach ? 
My application, as I see it now, will be in Active Halt mode with a wake-up period of 1 sec. Upon the wake-up it will be run during let's say 300us. During this run-mode or even one  in 5sec I may turn on the temperature sensor that needs just 20us to be measured. 
Any help  would be highly appreciated.
E.L.

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