Datasheet

PCF2129 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 7 — 19 December 2014 14 of 86
NXP Semiconductors
PCF2129
Accurate RTC with integrated quartz crystal for industrial applications
[1] Duty cycle definition: % HIGH-level time : % LOW-level time.
[2] Default value.
[3] The specified accuracy of the RTC can be only achieved with CLKOUT frequencies not equal to
32.768 kHz or if CLKOUT is disabled.
The duty cycle of the selected clock is not controlled, however, due to the nature of the
clock generation all but the 32.768 kHz frequencies are 50 : 50.
8.4 Register Aging_offset
8.4.1 Crystal aging correction
The PCF2129 has an offset register Aging_offset to correct the crystal aging effects
2
.
The accuracy of the frequency of a quartz crystal depends on its aging. The aging offset
adds an adjustment, positive or negative, in the temperature compensation circuit which
allows correcting the aging effect.
At 25 C, the aging offset bits allow a frequency correction of typically 1 ppm per AO[3:0]
value, from 7 ppm to +8 ppm.
Table 15. CLKOUT frequency selection
COF[2:0] CLKOUT frequency (Hz) Typical duty cycle
[1]
000
[2][3]
32768 60 : 40 to 40 : 60
001 16384 50 : 50
010 8192 50 : 50
011 4096 50 : 50
100 2048 50 : 50
101 1024 50 : 50
110 1 50 : 50
111 CLKOUT = high-Z -
Table 16. Aging_offset - crystal aging offset register (address 19h) bit allocation
Bit positions labeled as - are not implemented and return 0 when read.
Bit 7 6 5 4 3 2 1 0
Symbol - - - - AO[3:0]
Reset
value
- - - -1000
Table 17. Aging_offset - crystal aging offset register (address 19h) bit description
Bit positions labeled as - are not implemented and return 0 when read.
Bit Symbol Value Description
7 to 4 - - unused
3 to 0 AO[3:0] see Table 18
aging offset value
2. For further information, refer to the application note Ref. 3 “AN11186”.