Part # Application Notes Access Control Accessories Audio Adapters Broadcast Computer Power Supply Corded Terminals Cordless Terminal D datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: STM32F101xx and STM32F103xx RTC calibration


Part Details:

AN2604 Application note STM32F101xx and STM32F103xx RTC calibration Introduction The real-time clock (RTC) precision is a requirement in most embedded applications, but due to external environment ­ temperature change, frequency variation of the crystal that clocks the RTC ­ the RTC precision may not be as accurate as expected. The RTC embedded in the STM32F101xx and STM32F103xx comes with a digital clock calibration circuit suitable for manufacturing environments, that allows applications to compensate for crystal and temperature variations. This application note discusses the RTC calibration basics and explains how RTC calibration can be used to improve timekeeping accuracy. August 2007 Rev 1 1/14 www.st.com Contents AN2604 - Application note Contents 1 RTC calibration basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1 Crystal accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2 Calculating the needed amount of calibration . . . . . . . . . . . . . . . . . . . 10 3 Calculating calibration over a temperature range . . . . . . . . . . . . . . . . 11 4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2/14 AN2604 - Application note List of tables List of tables Table 1. Calibration table: compensation values in ppm and seconds per month (30 days) . . . . . . . 7 Table 2. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3/14 Document Outline 1 RTC calibration basics 1.1 Crystal accuracy Figure 1. Typical crystal accuracy plotted against temperature 1.2 Methodology Figure 2. RTC calibration clock output Table 1. Calibration table: compensation values in ppm and seconds per month (30 days) 2 Calculating the needed amount of calibration 3 Calculating calibration over a temperature range Figure 3. Crystal accuracy over a temperature range 4 Conclusion 5 Revision history Table 2. Document revision history


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