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| 型號： | ISL12022IBZ-T7A |
| 廠商： | Intersil |
| 文件頁數(shù)： | 20/29頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC RTC/CALENDAR TEMP SNSR 8SOIC |
| 應(yīng)用說明： | Addressing Power Issues in Real Time Clock Appls |
| 產(chǎn)品培訓模塊： | Solutions for Industrial Control Applications |
| 標準包裝： | 250 |
| 類型： | 時鐘/日歷 |
| 特點： | 警報器，夏令時，閏年，SRAM |
| 存儲容量： | 128B |
| 時間格式： | HH:MM:SS（12/24 小時） |
| 數(shù)據(jù)格式： | YY-MM-DD-dd |
| 接口： | I²C，2 線串口 |
| 電源電壓： | 2.7 V ~ 5.5 V |
| 電壓 - 電源，電池： | 1.8 V ~ 5.5 V |
| 工作溫度： | -40°C ~ 85°C |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 8-SOIC（0.154"，3.90mm 寬） |
| 供應(yīng)商設(shè)備封裝： | 8-SOIC |
| 包裝： | 帶卷 (TR) |
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ISL12022
27
FN6659.3
November 22, 2011
Applications Information
Crystal Oscillator Frequency Compensation
CRYSTAL CHARACTERISTICS
The ISL12022 device contains a complete system for adjusting
the frequency of the crystal oscillator to compensate for
temperature variation. A typical 32.768kHz crystal used with RTC
devices has a temperature versus frequency curve, as shown in
Figure 22.
Where
α is the temperature constant, with a typical value of
0.034 ppm/°C.
T0 is the turnover temperature of the crystal, which is the apex of
the parabolic curve. If the two factors
α and T0 are known, it is
possible to correct for crystal temperature error to very high
accuracy.
The crystal will have an initial accuracy error at room temperature,
typically specified at ±20°C. The other important characteristic is
the capacitances associated with the crystal. The load capacitance
is normally specified at 12.5pF, although it can be lower in some
cases. There is also a motional capacitance which affects the
ability of the load capacitance to pull the oscillation frequency, and
it is usually in the range of 2.2fF to 4.0fF.
RTC CLOCK CONTROL
The ISL12022 uses two mechanisms to adjust the RTC clock and
correct for the temperature error of the external crystal.
The Analog Trimming (AT) adjusts the load capacitance seen by
the crystal. Analog switches connect the appropriate capacitance
to change the frequency in increments of 1ppm. The adjustment
range for the ISL12022 is +32/-31ppm.
The AT can be further refined using the BETA register. the BETA
register function is to allow for changes in CM (motional
capacitance) which will affect the incremental frequency change
of the AT adjustment. A simple test procedure uses the BETA
register to bring the step size back to 1ppm.
Normally, the crystal frequency is adjusted at room temperature
to zero out the frequency error using the IATRxx register bits
(initial Analog Trimming). In addition, the IATRxx setting is varied
up and down to record the variation in oscillator frequency
compared to the step change in IATRxx. Once that value is known
then the BETA register is used to adjust the step size to be as
close to 1ppm per IATRxx step as possible. After that adjustment
is made, then any ISL12022 temperature compensation
adjustments will use a 1ppm change for each bit change in the
internal AT adjustment.
The Digital Trimming (DT) uses clock pulse add/subtract logic to
change the RTC timing during temperature compensation. The
DT steps are much coarser than the AT steps and are therefore
used for large adjustments. The DT steps are 30.5ppm, and the
range is from -305ppm to +305ppm. The Frequency Output
function will show the clock variation with DT settings, except for
the 32,768Hz setting which only shows the AT control.
ACTIVE TEMPERATURE COMPENSATION
The ISL12022 contains an intelligent logic circuit which takes the
temperature sensor digital value as the only input variable. It
then uses the register values for the crystal variables
α and T0,
and combines those with calibration from the BETA and ITR0
registers to produce “Final” values for the AT and DT, known as
FATR (Final AT Register) and FDTR (Final DT Register). Those AT
and DT values combine to directly compensate for the
temperature error shown in Figure 22.
The temperature sensor produces a new value every 60s (or up to
10 minutes in battery mode), which triggers the logic to calculate
a new AT/DT value set. For every temperature calculation result,
there can only be one corresponding AT/DT correction value.
Measuring Oscillator Accuracy
The best way to analyze the ISL12022 frequency accuracy is to
set the IRQ/FOUT pin for a specific frequency, and look at the
output of that pin on a high accuracy frequency counter (at least
7 digits accuracy). Note that the IRQ/FOUT is a drain output and
will require a pull-up resistor.
Using the 1.0Hz output frequency is the most convenient as the
ppm error is as expressed in Equation 8:
Other frequencies may be used for measurement but the error
calculation becomes more complex.
When the proper layout guidelines are observed, the oscillator
should start up in most circuits in less than 1s. When testing RTC
circuits, a common impulse is to apply a scope probe to the circuit
at the X2 pin (oscillator output) and observe the waveform. DO
NOT DO THIS! Although in some cases you may see a usable
waveform, due to the parasitics (usually 10pF to ground) applied
with the scope probe, there will be no useful information in that
waveform other than the fact that the circuit is oscillating. The X2
output is sensitive to capacitive impedance so the voltage levels
and the frequency will be affected by the parasitic elements in the
scope probe. Use the FOUT output and a frequency counter for the
most accurate results.
TEMPERATURE (°C)
-160
-140
-120
-100
-80
-60
-40
-20
0
-40 -30 -20 -10 0
10 203040506070 80
PP
M
FIGURE 22. RTC CRYSTAL TEMPERATURE DRIFT
Δf
α
T
(
T
0 )
2
–
=
(EQ. 7)
ppm error
F
(
OUT
1
) 1e6
–
=
(EQ. 8)
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ISL12022M | 制造商:INTERSIL 制造商全稱:Intersil Corporation 功能描述:Low Power RTC with Battery Backed SRAM, Integrated ±5ppm Temperature Compensation, and Auto Daylight Saving |
| ISL12022M_09 | 制造商:INTERSIL 制造商全稱:Intersil Corporation 功能描述:Low Power RTC with Battery Backed SRAM, Integrated ±5ppm Temperature Compensation, and Auto Daylight Saving |
| ISL12022M_10 | 制造商:INTERSIL 制造商全稱:Intersil Corporation 功能描述:Low Power RTC with Battery Backed SRAM,Integrated ±5ppm Temperature Compensation and Auto Daylight Saving |
| ISL12022MA | 制造商:INTERSIL 制造商全稱:Intersil Corporation 功能描述:Low Power RTC with Battery Backed SRAM, Integrated ±5ppm Temperature Compensation and Auto Daylight Saving |
| ISL12022MA_10 | 制造商:INTERSIL 制造商全稱:Intersil Corporation 功能描述:Low Power RTC with Battery Backed SRAM, Integrated ±5ppm Temperature Compensation and Auto Daylight Saving |
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