ISL12023 Datasheet, PDF (21/28 Pages) Intersil Corporation – Low Power RTC with Battery-Backed SRAM and Embedded Temp Compensation ±5ppm with Auto Daylight Saving

ISL12023
DST Day/Week Reverse
DstDwRv contains both the Day of the Week and the 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 degrees Centigrade (°C) by first converting from binary to
decimal, dividing by 2, and then subtracting 273d, as shown
in Equation 3.
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 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, which are fixed during factor test.
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 4:
NPPM = IPPM(ITR0,BETA) + ALPHA x (T-T0)²
NPPM = IPPM + CPPM
NPPM
=
I
P
P
M
+
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 ISL12023 has a preset turnover temperature
corresponding to the crystal in the module. This value is
recalled on initial power-up and should never be changed for
best temperature compensation performance, although the
user may override this preset value if so desired.
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.
21
FN6682.2
June 24, 2009