NXP Semiconductors PCA2125, PCA8565, PCF2123, PCF85x3 user manual

UM10301

User Manual for NXP Real Time Clocks PCF85x3, PCA8565

and PCF2123, PCA2125

Rev. 01 — 23 December 2008 User manual

Document information

Info Content

Keywords PCF8563, PCF8573, PCF8583, PCF8593, PCA8565, PCF2123,

PCA2125, PCF2120, RTC, real time clock, timekeeping, crystal,

32.768 kHz, backup.

Abstract This application note aims to assist a user of above mentioned Real Time

Clocks in achieving succesful design-in and application. It contains useful

hints with respect to electrical schematic and PCB layout as well as code

examples for the well established NXP PCF8563 and related Real Time

Clocks. Also the more recent Real Time Clocks PCF2123 and PCA2125

have been taken into account.

Contents

Main UM10301 User Manual for NXP Real Time Clocks PCF85x3, PCA8565 and PCF2123, PCA2125 Rev. 01 23 December 2008 User manual Contact information NXP Semiconductors UM10301 1. Introduction 2. Features Page 3. Comparison 3.1 Event counter mode User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 4. Power-on reset (POR) 5. Voltage-low detector 6. Oscillator NXP Semiconductors UM10301 Page Page CC CC C+ + = 1 = () () H Cf RCf L11234 101.2327682 1 2 6.1 Oscillation allowance R 6.2 Using an external oscillator 7. Crystal and crystal selection 7.1 Modes which dont work 7.2 Effect of temperature () [ [ ] ] [ 8. Capacitors and capacitor selection 9. Accuracy Page 10. Oscillator tuning Page 10.1 PCF2123 Offset register 11. Century and leap year, Daylight Saving Time 11.1 Century tracking 11.2 Year and leap year tracking 11.3 Daylight Saving Time (DST) 12. Initialization and setting of alarm and timer 12.1 Initialization of the RTC and setting the time User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 12.2 Alarm Page 12.3 Setting the timer NXP Semiconductors UM10301 13. Backup power supply 13.1 Lithium Primary cells Page 13.2 NiCd and NiMH secondary batteries 13.3 Capacitors 13.3.1 Charging the backup capacitor 13.3.2 Estimation of backup time with capacitor ( ) VVC t = () 14. PCB layout guidelines Page 15. Partial circuit switch down 16. Hints to keep power consumption low d = 0005 . 0 03 . 0 6 . 4 10 85 . 8 0007.0 109.148473.0 109.148473.0 C = = C Page 17. First period inaccuracy when using the timer Page 18. Timing requirements for I2C read and write I C interface Time counters Pre-scaler Watchdog Page 19. Troubleshooting 19.1 Oscillator startup time 19.2 Checking for oscillation 19.3 No communication via I2C-bus 19.4 Wrong time and date, wrong clock speed 20. References User manual Rev. 01 23 December 2008 51 of 52 21. Legal information 21.1 Definitions 21.2 Disclaimers 21.3 Trademarks 22. Contents