ISL12029 Intersil Corporation, ISL12029 Datasheet - Page 23

• Manufacturer Part Number: ISL12029
• Description: Real Time Clock/Calendar
• Manufacturer: Intersil Corporation

www.DataSheet4U.com
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. Figure 27 shows a suggested layout for the
ISL12029 or ISL12028 devices.
Citizen
Epson
Raltron
SaRonix
Ecliptek
ECS
Fox
FIGURE 27. SUGGESTED LAYOUT FOR INTERSIL RTC IN
MANUFACTURER
32.768kGz
XTAL1
SO-14
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
ISL12029
X1228
U1
PART NUMBER
R1 10k
TABLE 9. CRYSTAL MANUFACTURERS
C1
0.1µF
ISL12029
TEMP RANGE (°C)
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.
Oscillator Measurements
When a proper crystal is selected and the layout guidelines
above are observed, the oscillator should start up in most
circuits in less than one second. Some circuits may take slightly
longer, but startup should definitely occur in less than 5
seconds. When testing RTC circuits, the most common impulse
is to apply a scope probe to the circuit at the X2 pin (oscillator
output) and observe the waveform. DO NOT DO THIS!
Although in some cases you may see a usable waveform, due
to the parasitics (usually 10pF to ground) applied with the
scope probe, there will be no useful information in that
waveform other than the fact that the circuit is oscillating. The
X2 output is sensitive to capacitive impedance so the voltage
levels and the frequency will be affected by the parasitic
elements in the scope probe. Applying a scope probe can
possibly cause a faulty oscillator to start up, hiding other issues
(although in the Intersil RTCs, the internal circuitry assures
startup when using the proper crystal and layout).
The best way to analyze the RTC circuit is to power it up and
read the real time clock as time advances, or if the chip has
the IRQ/F
oscilloscope (after enabling it with the control register, and
using a pull-up resistor for the open-drain output).
Alternatively, the ISL12029 IRQ/F
checked by setting an alarm for each minute. Using the
pulse interrupt mode setting, the once-per-minute interrupt
functions as an indication of proper oscillation.
-40 to +85
-40 to +85
-40 to +85
-40 to +85
-10 to +60
-10 to +60
-40 to +85
OUT
output, look at the output of that pin on an
+25°C FREQUENCY TOLERANCE
DD
pin of the chip is mandatory,
OUT
- output can be
±20ppm
±20ppm
±20ppm
±20ppm
±20ppm
±20ppm
±20ppm
April 17, 2006
FN6206.4