isl12022m Intersil Corporation, isl12022m Datasheet - Page 21

• Manufacturer Part Number: isl12022m
• Description: Real Time Clock With Embedded Crystal, ??5ppm Accuracy
• Manufacturer: Intersil Corporation

• Bits 0,1,2 contain the Day of the week information which
• Bits 3, 4, 5 contain the Week of the Month information that
DST Date Reverse
DstDtRv controls which Date DST ends. The format for the
Date is the same as for the RTC register, from 1 to 31. The
default value for DST Date Reverse is 00h. The DstDtRv is
only effective if the DwRvE = 0.
DST Hour Reverse
DstHrRv controls the hour that DST ends. The RTC hour
and DstHrFd registers have the same formats except there
is no Military bit for DST hour. The user sets the DST hour
with the same format as used for the RTC hour (AM/PM or
MIL) but without the MIL bit, and the DST will still advance as
if the MIL bit were there. The default value for DST hour
Reverse is 00h.
TEMP Registers (TEMP)
The temperature sensor produces an analog voltage output
which is input to an A/D converter and produces a 10-bit
temperature value in degrees Kelvin. TK07:00 are the LSBs
of the code, and TK09:08 are the MSBs of the code. The
temperature result is actually the average of two successive
temperature measurements to produce greater resolution for
the temperature control. The output code can be converted
to degrees Centigrade by first converting from binary to
decimal, dividing by 2, and then subtracting 273d.
The practical range for the temp sensor register output is from
446d to 726d, or -50°C to +90°C. The temperature
compensation function is only guaranteed over -40°C to +85°C.
The TSE bit must be set to “1” to enable temperature sensing.
NPPM Registers (NPPM)
The NPPM value is exactly 2 times the net correction, in
ppm, required to bring the oscillator to 0ppm error. The value
is the combination of oscillator Initial Correction (IPPM) and
crystal temperature dependent correction (CPPM).
IPPM is used to compensate the oscillator offset at room
temperature and is controlled by the ITR0 and BETA registers.
This value is normally set during room temperature testing.
Temperature in °C
TK0L
TK0M
TEMP
sets the Day of the Week that DST ends. Note that Day of
the week counts from 0 to 6, like the RTC registers. The
default for the DST Reverse Day of the Week is 00h
(normally Sunday).
sets the week that DST ends. The range is from 1 to 5, and
Week 7 is used to indicate the last week of the month. The
default for the DST Reverse Week of the Month is 00h.
0
TK07 TK06 TK05 TK04 TK03 TK02 TK01 TK00
7
0
=
6
[(TK <9:0>)/2] - 273
0
5
TABLE 22.
21
0
4
0
3
0
2
TK09 TK08
1
(EQ. 3)
ISL12022M
0
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 2 times 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 the following equations:
NPPM = IPPM(ITR0, BETA) + ALPHA x (T-T0)2
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 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.
NPPM
NPPM
ALPHA
T
ADDR
=
T
2Ch
(
=
2 298
•
596
=
=
=
IPPM
IPPM
α 2048
+
TABLE 23. TURNOVER TEMPERATURE
)
7
0
•
XT0
+
XT0
+
+
CPPM
ALPHA
--------------------------------------------------- -
6
0
4096
5
0
•
(
T T0
–
XT4
4
)
2
XT3
3
XT2
2
December 18, 2008
XT1
1
(EQ. 4)
(EQ. 5)
FN6668.4
XT0
0