ISL12027 Intersil Corporation, ISL12027 Datasheet - Page 22

• Manufacturer Part Number: ISL12027
• Manufacturer: Intersil Corporation

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, 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 double 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. Figure 27 shows a suggested layout for the
ISL12027 or ISL12026 devices.
Frequency
Frequency Tolerance
Turnover Temperature
Operating Temperature Range
Parallel Load Capacitance
Equivalent Series Resistance
Citizen
Epson
Raltron
SaRonix
Ecliptek
ECS
Fox
MANUFACTURER
PARAMETER
CM201, CM202, CM200S
MC-405, MC-406
RSM-200S-A or B
32S12A or B
ECPSM29T-32.768K
ECX-306/ECX-306I
FSM-327
22
TABLE 7. CRYSTAL PARAMETERS REQUIRED FOR INTERSIL RTC’S
PART NUMBER
MIN
-40
20
TABLE 8. CRYSTAL MANUFACTURERS
32.768
TYP
12.5
25
ISL12027
MAX
±100
30
85
50
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 capacitor at the V
with a solid connection to ground (Figure 27).
TEMP RANGE
FIGURE 27. SUGGESTED LAYOUT FOR INTERSIL RTC IN SO-8
-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
UNITS
ppm
kHz
k
°C
°C
pF
Ω
Down to 20ppm if desired
Typically the value used for most crystals
For best oscillator performance
+25°C FREQUENCY TOLERANCE
DD
pin of the chip is mandatory,
NOTES
±20ppm
±20ppm
±20ppm
±20ppm
±20ppm
±20ppm
±20ppm
April 17, 2006
FN8232.3