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NXP Semiconductors PCF85x3 manual

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  • Page 1

    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, PCF 8593, PCA8565, PCF2123, PCA2125, PCF2120, RTC, real time clock, timekeeping, crystal, 32.768 kHz, backup. Abstract This application note aims to assist [...]

  • Page 2

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 2 of 52 Contact information For additional information, please visit: http://www.nxp .com For sales office addresse s, please send an email to: salesaddresses@nxp.com Revision histor[...]

  • Page 3

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 3 of 52 1. Introduction The real time clocks from NXP (previousl y Philips Semiconductors) have a long tradition and are used in numerous appli cation fields. Star ting from applicat[...]

  • Page 4

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 4 of 52 2. Features The NXP real-time clock p ortfolio includes types for low powe r, types for automotive and other high temperature applications and app lications that need additio[...]

  • Page 5

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 5 of 52 In BCD every digit of the decimal system is represented by a 4-bit grou p. For example: 157 10 = 0001 0101 0111 BCD This is not the same as binary repre sentation. It is clea[...]

  • Page 6

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 6 of 52 The PCA8565 and PCA2125 oscillato rs operate over a wider temperatu re range (up to 125 ºC) and are suitable for use in the harsh environ ments found within automobiles. Pow[...]

  • Page 7

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 7 of 52 Table 2. Comparison of six real time clocks PCx85x3 family PCx212x family Features PCF8563 PCA8565 PCF858 3 PCF8593 PCF2123 PCA2125 Unique features Very low power consumption[...]

  • Page 8

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 8 of 52 4. Power-on reset (POR) Traditionally a power-on reset circuit is a circuit that generate s a reset pulse once the supply voltage has reached a certain value upo n power-up. [...]

  • Page 9

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 9 of 52 The implementation in the PCF2123 is sli ghtly different. There a bit OS (Oscillator Stopped) is present instead of VL. The OS flag is set whenever th e oscillator is stopped[...]

  • Page 10

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 10 of 52 C STRAY is a result of parasitic capacitan ces due to PCB traces, IC pins etc. and is directly in parallel with C 0 of the crystal. In a practical sit uation care needs to b[...]

  • Page 11

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 11 of 52 The values used in practice will be a bit smaller than the theoretical ly required values due to parasitic capacitances present in the app lication which add to the external[...]

  • Page 12

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 12 of 52 capacitances. The external components of the oscillator have to be cho sen such that the actual value of C L matches the specified value of C L . If there is mismatch the cr[...]

  • Page 13

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 13 of 52 Now in order to determine the value of C L resulting from C IN , C OUT (plus C T if mounted) and C STRA Y it is necessary to realize t hat seen from the crystal, C IN and C [...]

  • Page 14

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 14 of 52 Taking the numbers from Table 4 yields for L 1 and Q: () () H C f L 11234 10 1 . 2 32768 2 1 2 1 15 2 1 2 0 1 = ⋅ ⋅ ⋅ = ⋅ ⋅ = − π π () () 42053 10 55 10 1 . 2 [...]

  • Page 15

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 15 of 52 6.1 Oscillation allo wance Fig 4 shows the Pierce oscillator schematic with the external crystal. For an oscillation to take place the real component of the oscillator imped[...]

  • Page 16

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 16 of 52 levels can be tuned such that they are simila r to those when the internal o scillator is used. Suppose that the RTC is supplied with 3 .3 V and that the amplitude of the ex[...]

  • Page 17

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 17 of 52 value is really too high start up problem s may occur, but up to 100 k Ω no start up problems are expecte d. See 6.1”Oscillation allowance”. The frequency accuracy of [...]

  • Page 18

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 18 of 52 The frequency of a typical crystal at a specific temperature T is given by: () [ ] 2 0 0 1 T T B f f − + = Further f 0 can be consid ered to consist of two compon ents as [...]

  • Page 19

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 19 of 52 handle this temperature. Generally metal can qu artzes are not recommended for high temperatures because the termal cycling (ex pansion of package) will cau se leakages in t[...]

  • Page 20

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 20 of 52 to +80 %. Its only redeeming feature is its hi gh permittivity which all ows high capacitance values, typically ranging from 1 nF to 4.7 µF. Good for bypass and coupling ap[...]

  • Page 21

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 21 of 52 Fig 8. Influences on time accuracy The various influence s indicated in Fig 8 are describe d below: 1. The line at the top indicates the frequency tolerance of the crystal i[...]

  • Page 22

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 22 of 52 5. Tuning C T will increase the initial accuracy, indicated by reducing th e range covered to the spread of C IN . Depending on how well C T is tuned, the initial spread can[...]

  • Page 23

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 23 of 52 Fig 9. Oscillator tuning Accuracy : In order to be able to adjust the clock wi th accuracy b etter than 1 s/day, the frequency counter used to check the output at CLKOUT sh [...]

  • Page 24

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 24 of 52 • In the datasheets of PCF8583 and PCF8593 the follo wing method is described: Using the alarm function (v ia the I 2 C-bus) a signal faster than 1 Hz can b e generated at[...]

  • Page 25

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 25 of 52 11. Centur y and leap year, Daylight Saving Time For details on how to implement century tr acking and year / leap year tracking, pl ease refer to the datasheets of the resp[...]

  • Page 26

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 26 of 52 12. Initialization and setting of alarm and timer Setting the clock is a straightforward proced ure, setting first the mode and then the actual time. This example is for the[...]

  • Page 27

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 27 of 52 Table 5. Setting the time and date Sequence of commands / data to be sent Binary (BCD) HEX Register Address Comments generate I 2 C start condition 1 0 1 0 0 0 1 0 A2 I 2 C [...]

  • Page 28

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 28 of 52 Binary (BCD) HEX Register Address Comments 0 0 0 0 1 0 0 1 09 word address 9 for minute alarm 0 0 0 1 0 1 0 1 15 09 minute alarm enabled and set to 15 minutes 1 0 0 0 0 0 0 [...]

  • Page 29

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 29 of 52 12.3 Setting the timer The internal timer is an 8-bit countdown ti mer which is controlled by the timer control register. The timer counts down from a software-loaded 8-bit [...]

  • Page 30

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 30 of 52 13. Backup power supply A real time clock is a clock that keeps track of the time as hum ans use it (hours, minutes, seconds, years etc.) and usually even when t he rest of [...]

  • Page 31

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 31 of 52 The mentioned IEC/UL standard st ates that circuits e mploying lithium batteries shall be designed to prevent forced cha rge and discharge if this would result in a hazard. [...]

  • Page 32

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 32 of 52 evaporation can be neglected. At elevated temperatures of fo r example 60 °C electrolyte evaporation will be much higher. Refe r to the manufacturer’s datasheet. Vendors [...]

  • Page 33

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 33 of 52 The recommende d trickle charge current for a NiCd or NiMH is expressed a s a fraction of C and is typically in the range C/50…C/20. Re fer to the datasheet of the selecte[...]

  • Page 34

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 34 of 52 If backup is only needed for a few minutes to deal with short interruptions in power, it is possible to use a small inexpensive ele ctrolytic capacitor. Supercaps can not be[...]

  • Page 35

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 35 of 52 Using C·V = I·t: ( ) RTC Cbackupend rt Cbackupsta backup I V V C t − ⋅ = Assuming that the PCF8563 is used, that V Cbackupstart = 3.3 V, that the RTC current consumpti[...]

  • Page 36

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 36 of 52 14. PCB layout guidelines The tuning fork crystal’s drive level is extremely lo w (< 1 μ W) and the input of the amplifier used in the oscillator (pin OSCI ) has a ver[...]

  • Page 37

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 37 of 52 (1) In practice the input capacitor C T will in most cases be a fixed capacitor Fig 14. PCB layout proposal for PCF8563 using leaded components Alternatively to the last poi[...]

  • Page 38

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 38 of 52 001aai849 SMD CR YST AL SD A CLK V DD SCL V SS OSCO OSCI INT lay er 1 ground via GND area PCF8563TS bypass capacitor oscillator capacitor guard ring Fig 15. PCB layout propo[...]

  • Page 39

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 39 of 52 Fig 16. Protection diode s . 16. Hints to keep power consumption low For some applications low power consu mption is a key requirement. Power consumption can be minimized by[...]

  • Page 40

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 40 of 52 • Access the RTC as little as possible in order to reduce the dynamic cu rrent consumption by the I 2 C-bus or SPI; • Disable the CLKOUT in battery backup mode. If CLKOU[...]

  • Page 41

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 41 of 52 b r P C t R ⋅ = 8473 . 0 (max) 002aac883 C b (pF) 0 600 400 200 8 12 4 16 20 R p(max) (k Ω ) 0 (1) (2) (3) (1) Standard-mode (2) Fast-mode (3) Fast-mode Plus Fig 17. R p([...]

  • Page 42

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 42 of 52 mgm665 SCL SDA V SS OSCI OSCO CLOCK CALENDAR PCF8563 SDA SCL MASTER TRANSMITTER/ RECEIVER V DD V DD SDA SCL RR V DD (I 2 C-bus) R: pull-up resistor R = 1 F t r C b 100 nF Fi[...]

  • Page 43

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 43 of 52 17. First period inaccurac y when using the timer This chapter describe s why the programmed del ay is not always exactly as expecte d and what to do in order to be as accur[...]

  • Page 44

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 44 of 52 The timer counts down from a software-loaded 8-bit binary value, n . Loading the counter with 0 effectively stops the timer. Values from 1 to 255 are valid. When the co unte[...]

  • Page 45

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 45 of 52 As an example, the desired timer period is 5 seco nds. If the timer source clock frequen cy is set to 1 Hz and n = 5, the minimum possible timer period will be (5-1) + 15.62[...]

  • Page 46

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 46 of 52 Fig 21. Block diagram I 2 C interface an d Time counters When there is no I 2 C activity the RTC is counting normally. Once an I 2 C read or write operation is initiated, th[...]

  • Page 47

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 47 of 52 Fig 22. Sequence of ev ents (example READ) From this follows: • A I 2 C read must be terminated within o ne second of initiation; • The RTC will automatically terminate [...]

  • Page 48

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 48 of 52 chapter could occur. First, the data could change while a single register is being read. Second, the data could change during the time between re ading two registers. Theref[...]

  • Page 49

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 49 of 52 19.3 No communication via I 2 C-bus When no communication with the RT C is possible, it is also not po ssible to set and read time. Normally the I 2 C-bus will not get stuck[...]

  • Page 50

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 50 of 52 19.4 Wrong time and date, wrong clock speed When writing into the RTC registers care has to be taken that only valid values are written. For example, seco nds only should go[...]

  • Page 51

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 UM10301_1 © NXP B.V. 2008. All rights r eserved. User manual Rev. 01 — 23 December 2008 51 of 52 21. Legal information 21.1 Definitions Draft — The document is a d raft version only . The content is still under internal review and subje ct to formal approv al, which m[...]

  • Page 52

    NXP Semiconductors UM10301 User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 Please be awar e that important notices concerni ng this document a nd the product(s) described herein, h ave been included in the section 'Leg al information'. © NXP B.V. 200 8. All righ ts reserved. For more information, please visit: http://www.nxp.com For sa[...]