Describes the digital calibration feature in TIMEKEEPER® products, this feature provides a simple and effective method to compensate for the temperature sensitivity of quartz crystals, improving system accuracy
This document describes the digital calibration feature available in STMicroelectronics TIMEKEEPER and serial real-time clock (RTC) products. It explains that while quartz oscillators are accurate, they are sensitive to temperature variations. The note details how the digital calibration circuit adds or subtracts counts from the oscillator divider circuit to compensate for these errors, offering a software-controlled alternative to external trim capacitors.
| Nominal Frequency | 32.768 kHz |
|---|---|
| Internal Capacitance | 12.5 pF |
| Calibration Range | +5.5 or -2.75 minutes per month |
The digital calibration circuit adds or subtracts counts from the oscillator divider circuit at the 256 Hz stage based on a value loaded into the control register.
The device is accurate within +1.53 minutes per month at 25 °C without calibration.
The peak of the accuracy curve corresponds to approximately 25 °C, which is known as the turnover temperature.
The real-time clock has an internal capacitance of 12.5 pF across the crystal input pins.