參數(shù)資料
型號(hào): ISL12028AIB27Z-T
廠商: INTERSIL CORP
元件分類(lèi): 時(shí)鐘/數(shù)據(jù)恢復(fù)及定時(shí)提取
英文描述: REAL TIME CLOCK, PDSO14
封裝: ROHS COMPLIANT, PLASTIC, MS-012AB, SOIC-14
文件頁(yè)數(shù): 16/29頁(yè)
文件大?。?/td> 579K
代理商: ISL12028AIB27Z-T
23
FN8233.8
August 9, 2010
A final application for the ATR control is in-circuit calibration
for high accuracy applications, along with a temperature
sensor chip. Once the RTC circuit is powered up with battery
backup, the IRQ/FOUT output is set at 32.768kHz and
frequency drift is measured. The ATR control is then
adjusted to a setting which minimizes drift. Once adjusted at
a particular temperature, it is possible to adjust at other
discrete temperatures for minimal overall drift, and store the
resulting settings in the EEPROM. Extremely low overall
temperature drift is possible with this method. The Intersil
evaluation board contains the circuitry necessary to
implement this control.
Layout Considerations
The crystal input at X1 has a very high impedance and will
pick up high frequency signals from other circuits on the
board. Since the X2 pin is tied to the other side of the crystal,
it is also a sensitive node. These signals can couple into the
oscillator circuit and produce double clocking or misclocking,
seriously affecting the accuracy of the RTC. Care needs to
be taken in layout of the RTC circuit to avoid noise pickup.
Figure 27 shows a suggested layout for the ISL12029 or
ISL12028 devices (R1 is not needed for the ISL12028).
.
TABLE 9. CRYSTAL PARAMETERS REQUIRED FOR INTERSIL RTC
PARAMETER
MIN
TYP
MAX
UNITS
NOTES
Frequency
32.768
kHz
Frequency Tolerance
±100
ppm
Down to 20ppm if desired
Turnover-Temperature
20
25
30
°C
Typically the value used for most crystals
Operating Temperature Range
-40
85
°C
Parallel Load Capacitance
12.5
pF
Equivalent Series Resistance
50
k
Ω
For best oscillator performance
TABLE 10. CRYSTAL MANUFACTURERS
MANUFACTURER
PART NUMBER
TEMP RANGE
(°C)
+25°C FREQUENCY
TOLERANCE
(ppm)
Citizen
CM201, CM202, CM200S
-40 to +85
±20
Epson
MC-405, MC-406
-40 to +85
±20
Raltron
RSM-200S-A or B
-40 to +85
±20
SaRonix
32S12A or B
-40 to +85
±20
Ecliptek
ECPSM29T-32.768K
-10 to +60
±20
ECS
ECX-306/ECX-306I
-10 to +60
±20
Fox
FSM-327
-40 to +85
±20
C1
0.1
F
XTAL1
U1
R1 10k
X1228
32.768kGz
FIGURE 27. SUGGESTED LAYOUT FOR INTERSIL RTC IN SO-14
ISL12028
32.768kHz
0.1F
C1
XTAL1
U1
R1
10k
ISL12028, ISL12028A
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