PCF2129A datasheet(13/68 Pages) NXP

13 / 68 page

PCF2129A_1

Product data sheet

Rev. 01 — 13 January 2010

13 of 68

NXP Semiconductors

PCF2129A

Integrated RTC, TCXO and quartz crystal

8.4 Register Aging_offset

8.4.1 Crystal aging correction

The PCF2129A has an aging offset register Aging_offset to correct the crystal aging

effects2.

The accuracy of the frequency of a quartz crystal depends on the aging. Crystal suppliers

usually specify the first year aging (typically

±1 ppm, maximum ±3 ppm) and/or the 10

years aging (typically

±5 ppm). The aging offset adds an offset, positive or negative, in the

temperature compensation circuits which allows to correct the aging effect.

The change in ppm per AO[3:0] value is different at different temperatures. At 25

°C, the

aging offset bits allow a frequency correction of typically 1 ppm per AO[3:0] value, from

−7ppm to +8 ppm.

[1]

Default value.

Table 11.

Aging_offset - crystal aging offset register (address 19h) bit description

Bit

Symbol

Value

Description

7 to 4 -

unused

3 to 0 AO[3:0]

see Table 12 aging offset value

For further information please refer to the application note Ref. 3 “AN10857”.

Table 12.

Frequency correction at 25

°C, typical

AO[3:0]

ppm

Decimal

Binary

00000

10001

20010

30011

40100

50101

60110

70111

81000

[1]

91001

−1

1010

−2

1011

−3

1100

−4

1101

−5

1110

−6

1111

−7

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