ISL12032IVZ-T Intersil, ISL12032IVZ-T Datasheet - Page 24

• Manufacturer Part Number: ISL12032IVZ-T
• Description: IC RTC LP BATT BACK SRAM 14TSSOP
• Manufacturer: Intersil
• Type: Clock/Calendar/NVSRAMr

Specifications of ISL12032IVZ-T

• Memory Size: 1K (128 x 8)
• Time Format: HH:MM:SS:hh (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-TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: ISL12032IVZ-TTR

Application Section
Oscillator Crystal Requirements
The ISL12032 uses a standard 32.768kHz crystal. Either
through hole or surface mount crystals can be used.
Table 28 lists some recommended surface mount crystals
and the parameters of each. This list is not exhaustive and
other surface mount devices can be used with the ISL12032
if their specifications are very similar to the devices listed.
The crystal should have a required parallel load capacitance
of 12.5pF and an equivalent series resistance of less than
50kΩ. The crystal’s temperature range specification should
match the application. Many crystals are rated for -10°C to
+60°C (especially through hole and tuning fork types), so an
appropriate crystal should be selected if extended
temperature range is required.
Layout Considerations
The crystal input at X1 has a very high impedance, and
oscillator circuits operating at low frequencies (such as
32.768kHz) are known to pick up noise very easily if layout
precautions are not followed. Most instances of erratic
clocking or large accuracy errors can be traced to the
susceptibility of the oscillator circuit to interference from
adjacent high speed clock or data lines. Careful layout of the
RTC circuit will avoid noise pickup and ensure accurate
clocking.
Two main precautions for crystal PC board layout should be
followed:
In addition, it is a good idea to avoid a ground plane under
the X1 and X2 pins and the crystal, as this will affect the load
capacitance and therefore the oscillator accuracy of the
circuit. If the F
away from the RTC device as well. The traces for the VBAT
1. Do not run the serial bus lines or any high speed logic
2. Add a ground trace around the crystal with one end
TABLE 28. SUGGESTED SURFACE MOUNT CRYSTALS
MANUFACTURER
lines in the vicinity of the crystal. These logic level lines
can induce noise in the oscillator circuit to cause
misclocking.
terminated at the chip ground. This will provide
termination for emitted noise in the vicinity of the RTC
device.
SaRonix
Ecliptek
Raltron
Citizen
Epson
ECS
Fox
OUT
pin is used as a clock, it should be routed
24
ECPSM29T-32.768K
MC-405, MC-406
PART NUMBER
RSM-200S
ECX-306
FSM-327
CM200S
32S12
ISL12032
and V
routed around the crystal.
AC Input Circuits
The AC input ideally will have a 2.5V
input, so this is the target for any signal conditioning circuitry
for the 50/60Hz waveform. Note that the peak-to-peak
amplitude can range from 1V
best to keep the max signal level just below V
input provides DC offset so AC coupling with a series
capacitor is advised.
If the AC power supply has a transformer, the secondary
output can be used for clocking with a resistor divider and
series AC coupling capacitor. A sample circuit is shown in
Figure 12. Values for R
peak-to-peak range on the secondary voltage in order to
match the input of the ISL12032. C
up to 300Hz or so, and in most cases, 0.47µF should be the
selected value for a ±20% tolerance device.
The AC input to the IS12032 can be damaged if subjected to
a normal AC waveform when V
happen in circuits where there is a local LDO or power
switch for placing circuitry in standby, while the AC main is
still switched ON. Figure 11 shows a modified version of the
Figure 12 circuit, which uses an emitter follower to
essentially turn off the AC input waveform if the V
goes down.
Using the ISL12032 with No AC Input
Some applications may need all the features of the
ISL12032 but do not have access to the power line AC clock,
or do not need the accuracy provided by that clock. In these
cases there is no problem using the crystal oscillator as the
primary clock source for the device.
The user must simply set the ACENB bit in register 13h to
“1”, which disables the AC input pin and forces the device to
use the crystal oscillator exclusively for the RTC and F
clock source. Setting this bit to “1” also will cause the
ACRDY bit in the SRAC register to be set to “1”, indicating
that there can be no fault with the AC input clock since it is
not used.
DD
pins can be treated as a ground, and should be
1
/R
2
are chosen depending on the
P-P
DD
up to V
is powered down. this can
IN
P-P
can be sized to pass
DD
sine wave at the
, although it is
DD
. The AC
DD
April 16, 2009
supply
FN6618.2
OUT