Accurate RTC using HSI

[daniel2]

Posted on June 23, 2014 at 21:14

I'm using the SMT32F030 with 48MHz internal clock. I've configured the RTC and noticed it is about 8% fast. Is there a way to make this more accurate through calibration of some sort? Will that have to be done from part to part? Or is the only solution using an external crystal?

[Tesla DeLorean]

Posted on June 23, 2014 at 21:22

For the RTC you can play games with the Prescalers, other STM32 parts permit you to time internal clocks via one or two TIM units, or export them via an MCO pin (PA8). You might want to check the manuals for calibration/trim options.

The internal RC based clocks are also going to be impacted by temperature and voltage, on top of any process based differences. Depending on the accuracy you're looking for you're going to need external crystals, or oscillators, TCXO, etc. My experiences with LSI is that it's not particularly stable.