ISL12022 INTERSIL [Intersil Corporation], ISL12022 Datasheet - Page 22

• Manufacturer Part Number: ISL12022
• Manufacturer: INTERSIL [Intersil Corporation]

The CPPM compensates the oscillator frequency fluctuation
over temperature. It is determined by the temperature (T),
crystal curvature parameter (ALPHA), and crystal turnover
temperature (XT0). T is the result of the temp sensor/ADC
conversion, whose decimal result is 2x the actual
temperature in Kelvin. ALPHA is from either the ALPHA
(cold) or ALPHAH (hot) register depending on T, and XT0 is
from the XT0 register.
NPPM is governed by Equation 5:
NPPM = IPPM(ITR0,BETA) + ALPHA x (T-T0)
where:
T is the reading of the ADC, result is 2 x temperature in
degrees Kelvin.
or
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.
The ISL12022 allows setting the turnover temperature so
that temperature compensation can more exactly fit the
curve of a crystal. 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.
NPPM
NPPM
ALPHA
T
ADDR
=
T
2Ch
(
=
2 298
•
596
=
=
=
IPPM
IPPM
α 2048
+
TABLE 23. TURNOVER TEMPERATURE
)
0
7
XT<4:0>
•
XT0
+
01101
01100
01011
01010
01111
01110
XT0
+
+
CPPM
ALPHA
--------------------------------------------------- -
6
0
TABLE 24. XT0 VALUES
4096
5
0
•
(
T T0
22
–
XT4
4
TURNOVER TEMPERATURE
)
2
XT3
3
XT2
2
32.5
32.0
31.5
30.5
31
30
2
XT1
1
(EQ. 5)
(EQ. 6)
XT0
0
ISL12022
ALPHA Hot Register (ALPHAH)
The Alpha Hot variable is 7 bits and is defined as the
temperature coefficient of Crystal from the T0 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/°C
Cold version, a scaled version of the absolute value of this
coefficient is used in order to get an integer value. Therefore,
AlphaH<7:0> is defined as the (|Actual AlphaH Value| x 2048)
and converted to binary. For example, a crystal with AlphaH of
-0.034ppm/°C
converted to a binary number of 0100110b.
ADDR
2Dh
D
7
XT<4:0>
TABLE 24. XT0 VALUES (Continued)
01001
01000
00110
00101
00100
00011
00010
00001
00000
10000
10001
10010
10011
10100
10101
10110
11000
11001
11010
ALP_H6 ALP_H5 ALP_H4 ALP_H3 ALP_H2 ALP_H1 ALP_H0
00111
10111
11011
11100
11101
11110
11111
2
2
is first scaled (|2048*(-0.034)| = 70d) and then
6
,with a typical value of -0.034. Like the Alpha
TABLE 25. ALPHAH REGISTER
5
4
TURNOVER TEMPERATURE
3
29.5
29.0
28.5
28.0
27.5
27.0
26.5
26.0
25.5
25.0
25.0
24.5
24.0
23.5
23.0
22.5
22.0
21.5
21.0
20.5
20.0
19.5
19.0
18.5
18.0
17.5
2
June 23, 2009
FN6659.2
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