pcf2127a NXP Semiconductors, pcf2127a Datasheet - Page 14

• Manufacturer Part Number: pcf2127a
• Description: Integrated Rtc, Tcxo And Quartz Crystal
• Manufacturer: NXP Semiconductors

NXP Semiconductors
2.
PCF2127A_1
Product data sheet
For further information please refer to the application note
8.4.1 Crystal aging correction
8.4 Register Aging_offset
Table 11.
The PCF2127A has an aging offset register Aging_offset to correct the crystal aging
effects
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
−7 ppm to +8 ppm.
Table 12.
[1]
Bit
7 to 4 -
3 to 0 AO[3:0]
AO[3:0]
Decimal
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Default value.
2
Symbol
.
Aging_offset - crystal aging offset register (address 19h) bit description
Frequency correction at 25 °C, typical
Rev. 01 — 21 January 2010
Ref. 3
Value
-
see
Table 12
“AN10857”.
Binary
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
Description
unused
aging offset value
Integrated RTC, TCXO and quartz crystal
[1]
PCF2127A
ppm
+8
+7
+6
+5
+4
+3
+2
+1
0
−1
−2
−3
−4
−5
−6
−7
© NXP B.V. 2010. All rights reserved.
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