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Real Time ClockHow to use
The accuracy of time by RTC ICs depends on several factors as shown below:
Supposed that the gain or loss of the time set by a Xtal osccillator, RTC_IC, and a PCB is "X", then, the accuracy of time,
X = ±  ±  ±  ±  ±  ± 
 is defined as specification of a Xtal oscillator. Generally, ±10ppm or ±20ppm tolerance is common. Supposed that ±20ppm- Xtal oscillator is selected.
 depends on the operating temperature around the application, here, supposed that the temperature is room temperature, around 25 degreeC. In that case, the tolerance of this part is ±0ppm.
 Generally, frequency change over 1 year is commonly ±10ppm for a Xtal oscillator. But initially, this part is also ±0ppm.
 is mentioned as ±5ppm to ±10ppm in our datasheet, but actually, the dispersion is very small, so supposed that this tolerance is considered as ±5ppm.
 As shown in the typical characteristics in the datasheet, in case of Ricoh RTC_ICs, this tolerance can be almost ignored.
 Supposed that this tolerance is considered as ±5ppm.
X = ±  ±  ±  ±  ±  ±  = ±20ppm ±0ppm ±0ppm ±5ppm ±0ppm ±5ppm = ±30ppm
In monthly rate,
±30ppm x 60sec. x 60min. x 24hrs. x 31days = ±80sec./month
To improve the accuracy of time, fine adjustment is necessary after all components mounting on board.
By fine adjustment, the errors caused by     can be cancelled.
As for our module, R2025, R2045, a Xtal oscillator is built in and fine adjustment has been done before shipping to the users, and realized the time accuracy ±5ppm (at 25°C). In monthly rate, 13.4sec./month.