ISL12029IB27AZ Intersil, ISL12029IB27AZ Datasheet - Page 24

• Manufacturer Part Number: ISL12029IB27AZ
• Description: IC RTC/CALENDAR EEPROM 14-SOIC
• Manufacturer: Intersil
• Type: Clock/Calendar/Supervisor/EEPROMr

Specifications of ISL12029IB27AZ

• Memory Size: 4K (512 x 8)
• Time Format: HH:MM:SS (12/24 hr)
• Date Format: YY-MM-DD-dd
• Interface: I²C, 2-Wire Serial
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 14-SOIC (3.9mm Width), 14-SOL
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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
device.
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 start-up should definitely occur in less than 5s.
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
start-up when using the proper crystal and layout).
FIGURE 27. SUGGESTED LAYOUT FOR INTERSIL RTC IN
XTAL
32.768kGz
32.768kGz
XTAL1
SO-14
24
DD
ISL12029
X1228
pin of the chip is mandatory,
U1
U1
R1 10k
R1 10k
ISL12029, ISL12029A
C1
0.1µF
C1
0.1µF
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 are an indication of proper oscillation.
Backup Battery Operation
Many types of batteries can be used with the Intersil RTC
products. 3.0V or 3.6V Lithium batteries are appropriate, and
sizes are available that can power a Intersil RTC device for up
to 10 years. Another option is to use a supercapacitor for
applications where V
periods of time. Depending on the value of supercapacitor
used, backup time can last from a few days to two weeks (with
>1F). A simple silicon or Schottky barrier diode can be used in
series with V
connected to the V
very low leakages, <1µA desirable. Do not use the diode to
charge a battery (especially lithium batteries!).
Note that whether a battery or supercap is used, if the V
voltage drops below the data sheet minimum of 1.8V and the
V
RESET output may stay low and the I
not operate. The V
to 0V together to allow normal operation again.
There are two possible modes for battery backup operation,
Standard and Legacy mode. In Standard mode, there are no
operational concerns when switching over to battery backup
since all other devices functions are disabled. Battery drain
is minimal in Standard mode, and return to Normal V
powered operation is predictable. In Legacy modes the V
pin can power the chip if the voltage is above V
V
communicate with the device under battery backup, but the
supply current drain is much higher than the Standard mode
and backup time is reduced. In this case if alarms are used
in backup mode, the IRQ/F
connected to V
the default mode is the Standard mode.
2.7V TO 5.5V
DD
TRIP
FIGURE 28. SUPERCAPACITOR CHARGING CIRCUIT
power cycles to 0V then back to V
. This makes it possible to generate alarms and
OUT
DD
output, look at the output of that pin on an
BAT
to charge the supercapacitor, which is
BAT
BAT
voltage source. During initial power-up
DD
V
DD
pin. Try to use Schottky diodes with
and V
may disappear intermittently for short
V
SS
OUT
V
DD
BAT
pull-up resistor must be
power will need to be cycled
OUT
2
- output can be
C communications will
DD
voltage, then the
SUPERCAPACITOR
December 16, 2010
DD
and
DD
FN6206.10
BAT
BAT