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X1227S8I-2.7 参数 Datasheet PDF下载

X1227S8I-2.7图片预览
型号: X1227S8I-2.7
PDF下载: 下载PDF文件 查看货源
内容描述: 实时时钟/日历/ CPU监控器, EEPROM [Real Time Clock/Calendar/CPU Supervisor with EEPROM]
分类和应用: 计时器或实时时钟微控制器和处理器外围集成电路光电二极管监控可编程只读存储器电动程控只读存储器电可擦编程只读存储器
文件页数/大小: 28 页 / 442 K
品牌: XICOR [ XICOR INC. ]
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X1227  
APPLICATION SECTION  
cally 25 deg C, and a peak drift of >110ppm occurs at  
the temperature extremes of –40 and +85 deg C. It is  
possible to address this variable drift by adjusting the  
load capacitance of the crystal, which will result in pre-  
dictable change to the crystal frequency. The Xicor  
RTC family allows this adjustment over temperature  
since the devices include on-chip load capacitor trim-  
ming. This control is handled by the Analog Trimming  
Register, or ATR, which has 6 bits of control. The load  
capacitance range covered by the ATR circuit is  
approximately 3.25pF to 18.75pF, in 0.25pf incre-  
ments. Note that actual capacitance would also  
include about 2pF of package related capacitance. In-  
circuit tests with commercially available crystals dem-  
onstrate that this range of capacitance allows fre-  
quency control from +116ppm to –37ppm, using a  
12.5pF load crystal.  
CRYSTAL OSCILLATOR AND TEMPERATURE  
COMPENSATION  
Xicor has now integrated the oscillator compensation  
circuity on-chip, to eliminate the need for external com-  
ponents and adjust for crystal drift over temperature  
and enable very high accuracy time keeping (<5ppm  
drift.  
The Xicor RTC family uses an oscillator circuit with on-  
chip crystal compensation network, including adjust-  
able load-capacitance. The only external component  
required is the crystal. The compensation network is  
optimized for operation with certain crystal parameters  
which are common in many of the surface mount or  
tuning-fork crystals available today. Table 6 summa-  
rizes these parameters.  
In addition to the analog compensation afforded by the  
adjustable load capacitance, a digital compensation  
feature is available for the Xicor RTC family. There are  
three bits known as the Digital Trimming Register or  
DTR, and they operate by adding or skipping pulses in  
the clock signal. The range provided is 30ppm in  
increments of 10ppm. The default setting is 0ppm. The  
DTR control can be used for coarse adjustments of  
frequency drift over temperature or for crystal initial  
accuracy correction.  
Table 7 contains some crystal manufacturers and part  
numbers that meet the requirements for the Xicor RTC  
products.  
The turnover temperature in Table 6 describes the  
temperature where the apex of the of the drift vs. tem-  
perature curve occurs. This curve is parabolic with the  
drift increasing as (T-T0)2. For an Epson MC-405  
device, for example, the turnover temperature is typi-  
Table 6. Crystal Parameters Required for Xicor RTC’s  
Parameter  
Min  
Typ  
Max  
Units  
kHz  
Notes  
Frequency  
32.768  
Freq. Tolerance  
100  
30  
ppm  
Down to 20ppm if desired  
Typically the value used for most  
crystals  
Turnover Temperature  
20  
25  
°C  
Operating Temperature Range  
Parallel Load Capacitance  
Equivalent Series Resistance  
-40  
85  
°C  
pF  
kΩ  
12.5  
50  
For best oscillator performance  
Table 7. Crystal Manufacturers  
Manufacturer  
Citizen  
Part Number  
CM201, CM202, CM200S  
MC-405, MC-406  
RSM-200S-A or B  
32S12A or B  
Temp Range  
-40 to +85°C  
-40 to +85°C  
-40 to +85°C  
-40 to +85°C  
-10 to +60°C  
-10 to +60°C  
-40 to +85°C  
+25°C Freq Toler.  
20ppm  
Epson  
20ppm  
Raltron  
SaRonix  
Ecliptek  
ECS  
20ppm  
20ppm  
ECPSM29T-32.768K  
ECX-306/ECX-306I  
FSM-327  
20ppm  
20ppm  
Fox  
20ppm  
Characteristics subject to change without notice. 21 of 28  
REV 1.1.20 1/13/03  
www.xicor.com  
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