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Run-time calibration of watch crystals

Posted: 22 Oct 2008 ?? ?Print Version ?Bookmark and Share

Keywords:clock application? watch crystal? calendar circuit? application note?

For watch and timekeeping applications, 32.768kHz crystals with an accuracy close to 20ppm are common, but 20ppm translates to a 0.65536Hz frequency deviation, or a whopping 51.8 seconds error per month. This error only accounts for variation in crystal properties. Other significant sources include temperature, aging, component selection and layout.

In this application note, we discuss errors associated with low-cost watch crystals used in Real-Time Clock and Calendar (RTCC) applications and methods to overcome these errors. We also discuss a unique built-in calibration feature in Microchip Technology's Real-Time Clock and Calendar circuits, which minimizes these errors during run time.

View the PDF document for more information.

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