ISL12022MIBZ-T7A Datasheet, PDF (23/31 Pages) Intersil Corporation – Low Power RTC with Battery Backed SRAM, Integrated ±5ppm Temperature Compensation and Auto Daylight Saving

ISL12022M
NPPM is governed by Equations 4 and 5:
NPPM = IPPM(ITRO,BETA) + ALPHA × (T-T0)²
NPPM = IPPM + CPPM
NPPM
=
I
P
P
M
+
-^A----^L----^P----^H-----^A------^•----⁽--^T-----–-----^T----⁰----⁾--²-
4096
(EQ. 4)
where
ALPHA = α • 2048
T is the reading of the ADC, result is 2 x temperature in degrees
Kelvin.
T = (2 • 298) + XT0
(EQ. 5)
or T = 596 + XT0
Note that NPPM can also be predicted from the FATR and FDTR
register by the relationship (all values in decimal):
NPPM = 2*(BETA*FATR - (FDTR-16)
XT0 Registers (XT0)
TURNOVER TEMPERATURE (XT<3:0>)
The apex of the Alpha curve occurs at a point called the turnover
temperature, or XT0. Crystals normally have a turnover
temperature between +20°C and +30°C, with most occurring
near +25°C.
TABLE 23. TURNOVER TEMPERATURE
ADDR 7
6
5
4
3
2
1
0
2Ch
0
0
0 XT4 XT3 XT2 XT1 XT0
The ISL12022M has a preset Turnover temperature
corresponding to the crystal in the module. This value is recalled
on initial power-up and is preset in device production. It is READ
ONLY and cannot be overwritten by the user.
Table 24 shows the values available, with a range from +17.5°C
to +32.5°C in +0.5°C increments. The default value is 00000b
or +25°C.
TABLE 24. XT0 VALUES
XT<4:0>
TURNOVER TEMPERATURE
01111
32.5
01110
32.0
01101
31.5
01100
31
01011
30.5
01010
30
01001
29.5
01000
29.0
00111
28.5
00110
28.0
00101
27.5
00100
27.0
00011
26.5
TABLE 24. XT0 VALUES (Continued)
XT<4:0>
TURNOVER TEMPERATURE
00010
26.0
00001
25.5
00000
25.0
10000
25.0
10001
24.5
10010
24.0
10011
23.5
10100
23.0
10101
22.5
10110
22.0
10111
21.5
11000
21.0
11001
20.5
11010
20.0
11011
19.5
11100
19.0
11101
18.5
11110
18.0
11111
17.5
ALPHA Hot Register (ALPHAH)
TABLE 25. ALPHAH REGISTER
ADDR 7 6
5
4
3
2
1
0
2Dh D ALP_H6 ALP_H5 ALP_H4 ALP_H3 ALP_H2 ALP_H1 ALP_H0
The ALPHA Hot variable is 7 bits and is defined as the temperature
coefficient of Crystal from the XT0 value to +85°C (both Alpha Hot
and Alpha Cold must be programmed to provide full temperature
compensation). It is normally given in units of ppm/°C², with a
typical value of -0.034. Like the ALPHA Cold version, a scaled
version of the absolute value of this coefficient is used in order to
get an integer value. Therefore, ALP_H <7:0> is defined as the
(|Actual Alpha Hot Value| x 2048) and converted to binary. For
example, a crystal with Alpha Hot of -0.034ppm/°C² is first scaled
(|2048*(-0.034)| = 70d) and then converted to a binary number
of 01000110b.
The practical range of Actual ALPHAH values is from -0.020 to
-0.060.
The ISL12022M has a preset ALPHAH value corresponding to the
crystal in the module. This value is recalled on initial power-up
and is preset in device production. It is READ ONLY and cannot
be overwritten by the user.
23
FN6668.9
June 20, 2012