ISL12028 Intersil Corporation, ISL12028 Datasheet - Page 23

• Manufacturer Part Number: ISL12028
• 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, the IRQ/F
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. Below in Figure 27 is a suggested layout for the
ISL12029 or ISL12028 devices.
FIGURE 27. SUGGESTED LAYOUT FOR INTERSIL RTC IN SO-14
Citizen
Epson
Raltron
SaRonix
Ecliptek
ECS
Fox
MANUFACTURER
32.768kHz
32.768kGz
XTAL1
OUT
output is set at 32.768kHz and
CM201, CM202, CM200S
MC-405, MC-406
RSM-200S-A or B
32S12A or B
ECPSM29T-32.768K
ECX-306/ECX-306I
FSM-327
23
ISL12028
X1228
U1
PART NUMBER
R1 10k
TABLE 9. CRYSTAL MANUFACTURERS
C1
0.1µF
ISL12028
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.
For other RTC products, the same rules stated above should
be observed, but adjusted slightly since the
packages and pinouts are slightly different.
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 FREQUENCY TOLERANCE
DD
pin of the chip is mandatory,
±20ppm
±20ppm
±20ppm
±20ppm
±20ppm
±20ppm
±20ppm
April 17, 2006
FN8233.3