參數資料
型號: X1288V14Z
廠商: INTERSIL CORP
元件分類: XO, clock
英文描述: 2-Wire⑩ RTC Real Time Clock/Calendar/CPU Supervisor with EEPROM
中文描述: 1 TIMER(S), REAL TIME CLOCK, PDSO14
封裝: ROHS COMPLIANT, PLASTIC, TSSOP-14
文件頁數: 23/27頁
文件大小: 425K
代理商: X1288V14Z
23
FN8102.3
April 14, 2006
Table 7. Crystal Parameters Required for Intersil RTC’s
Table 8. Crystal Manufacturers
A final application for the ATR control is in-circuit cali-
bration for high accuracy applications, along with a
temperature sensor chip. Once the RTC circuit is pow-
ered up with battery backup, the PHZ 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.
For more detailed operation see Intersil’s application
note AN154 on Intersil’s website at www.intersil.com.
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 dou-
ble clocking or mis-clocking, seriously affecting the
accuracy of the RTC. Care needs to be taken in layout
of the RTC circuit to avoid noise pickup. Below in Fig-
ure 19 is a suggested layout for the X1286 or X1288
devices.
The X1 and X2 connections to the crystal are to be
kept as short as possible. A thick ground trace around
the crystal is advised to minimize noise intrusion, but
ground near the X1 and X2 pins should be avoided as
it will add to the load capacitance at those pins. Keep
in mind these guidelines for other PCB layers in the
vicinity of the RTC device. A small decoupling capaci-
tor at the Vcc pin of the chip is mandatory, with a solid
connection to ground.
The X1286 product has a special consideration. The
PHZ/IRQ- pin on the 8-lead SOIC package is located
next to the X2 pin. When this pin is used as a fre-
quency output (PHZ) and is set to 32.768kHz output
frequency, noise can couple to the X1 or X2 pins and
cause double-clocking. The layout in Figure 19 can
help minimize this by running the PHZ output away
Parameter
Min
Typ
32.768
Max
Units
kHz
ppm
°C
Notes
Frequency
Freq. Tolerance
Turnover Temperature
±100
30
Down to 20ppm if desired
Typically the value used for most
crystals
20
25
Operating Temperature Range
Parallel Load Capacitance
Equivalent Series Resistance
-40
85
°C
pF
k
12.5
50
For best oscillator performance
Manufacturer
Citizen
Epson
Raltron
SaRonix
Ecliptek
ECS
Fox
Part Number
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
±20ppm
±20ppm
±20ppm
±20ppm
±20ppm
±20ppm
CM201, CM202, CM200S
MC-405, MC-406
RSM-200S-A or B
32S12A or B
ECPSM29T-32.768K
ECX-306/ECX-306I
FSM-327
C1
0.1μF
XTAL1
32.768kGz
U1
R1 10k
X1286/X1288
FIGURE 19. SUGGESTED LAYOUT FOR INTERSIL RTC IN SO-8
X1288
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