内部时钟本身是有一些误差的,这点在datasheet以及RM中也有讲,
On-chip RC oscillator range of 31.25–39.0625 kHz as the reference of FLL input
with 0.2% trim step and 1% accuracy across temperature range of 0 °C to 70 °C and
1.5% accuracy across temperature of –40 °C to 105 °C.
所以,如果需要精确的时钟,还是需要使用外部时钟。