I'm working in some projects with an RTC. I'm using the PCF85063A. The problem is: the RTC counter is advancing from real time about 2 minutes per week. I searched for hardware and firmware errors, and the only thing that caused me doubts was the oscillator's load capacitors.
As you can see the crystal frequency tolerance is 20ppm, it means about 1 minute of error per month in clock counter.
The RTC have embedded oscillator load capacitors:
I'm actually using 7pF because it is the default value. I found nothing about oscillator load capacitor vs oscillating frequency variation.
Can someone explain the relationship about my problem and the load capacitors, or is there something else I'm not considering?