ISL12022MR5421 Datasheet, PDF (23/29 Pages) Intersil Corporation – Low Power RTC with Battery Backed SRAM, Integrated 5ppm

ISL12022MR5421
Week of the Month data for DST Reverse control. DST
can be controlled either by actual date or by setting both
the Week of the month and the Day of the Week.
DstDwRvE sets the priority of the Day/Week over the
Date. For DstDwRvE = 1, Day/Week is the priority. You
must have the correct Day of Week entered in the RTC
registers for the Day/Week correction to work properly.
• Bits 0, 1, 2 contain the Day of the week information
which 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).
• Bits 3, 4, 5 contain the Week of the Month information
that 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.
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 °C by first converting
from binary to decimal, dividing by 2, and then
subtracting 273d.
Temperature in °C = [(TK <9:0>)/2] - 273
(EQ. 3)
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.
TABLE 22.
TEMP 7
6
5
4
3
2
1
0
TK0L TK07 TK06 TK05 TK04 TK03 TK02 TK01 TK00
TK0M 0
0
0
0
0
0
TK09 TK08
NPPM Registers (NPPM)
The NPPM value is exactly 2x 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.
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 Equations 4 and 5:
NPPM = IPPM(ITR0, BETA) + ALPHA x (T-T0)2
NPPM = IPPM + CPPM
NPPM
=
IPPM
+
A_-----L_----P_----H_-----A_------•_----(_--T_{-----–-----}T_----0_----)_--²_-
4096
where
(EQ. 4)
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 ISL12022MR5421 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.
23
FN7576.1
June 4, 2010