FN6659 datasheet(24/32 Pages) RENESAS

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ISL12022

FN6659 Rev.3.01

Page 24 of 32

Oct 24, 2019

NPPM is governed by Equation 5:

where:

T is the reading of the ADC, result is 2 x temperature in degrees

Kelvin.

Note that NPPM can also be predicted from the FATR and FDTR

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.

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/°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, 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/°C2 is first scaled

(|2048*(-0.034)| = 70d) and then converted to a binary number

of 0100110b.

The practical range of Actual AlphaH values is from

-0.020 to -0.060.

The ALPHAH register should only be changed while the TSE

(Temp Sense Enable) bit is “0”.

TABLE 23. TURNOVER TEMPERATURE

ADDR

7654321

2Ch

XT4XT3

XT2XT1

XT0

TABLE 24. XT0 VALUES

XT<4:0>

TURNOVER TEMPERATURE

01111

32.5

01110

32.0

01101

31.5

01100

01011

30.5

01010

01001

29.5

01000

29.0

00111

28.5

00110

28.0

00101

27.5

00100

27.0

00011

26.5

00010

26.0

NPPM

IPPM ALPHA

T T0

–





4096

----------------------------------------------------

(EQ. 5)

NPPM

IPPM CPPM

NPPM

IPPM ITRO,BETA

 ALPHA

T-T0





ALPHA

 2048



T2 298



 XT0

(EQ. 6)

or T

596 XT0

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

TABLE 25. ALPHAH REGISTER

ADDR

765

432

2Dh

ALP_H6 ALP_H5 ALP_H4 ALP_H3 ALP_H2 ALP_H1 ALP_H0

TABLE 24. XT0 VALUES (Continued)

XT<4:0>

TURNOVER TEMPERATURE

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