ISL12024IRTC Datasheet, PDF (7/24 Pages) Intersil Corporation – Real-Time Clock/Calendar

ISL12024IRTC
Description
The ISL12024IRTCZ device is a real-time clock with
clock/calendar, 64-bit unique ID, two polled alarms with
integrated 512x8 EEPROM, oscillator compensation, and
battery backup switch.
The oscillator uses an external, low-cost 32.768kHz crystal.
All compensation and trim components are integrated on the
chip. This eliminates several external discrete components
and a trim capacitor, saving board area and component cost.
The real-time clock keeps track of time with separate
registers for hours, minutes and seconds. The calendar has
separate registers for date, month, year and day-of-week.
The calendar is correct through 2099, with automatic leap
year correction.
The 64-bit unique ID is a random numbers programmed,
verified and locked at the factory and it is only accessible for
reading and cannot be altered by the customer.
The Dual Alarms can be set to any clock/calendar value for a
match. For instance, every minute, every Tuesday, or 5:23
AM on March 21. The alarms can be polled in the Status
Register or can provide a hardware interrupt (IRQ/F_OUT
Pin). There is a pulse mode for the alarms allowing for
repetitive alarm functionality.
The IRQ/F_OUT pin may be software selected to provide a
frequency output of 1Hz, 4096Hz, or 32,768Hz or inactive.
The device offers a backup power input pin. This V_BAT pin
allows the device to be backed up by battery or Super Cap.
The entire ISL12024IRTCZ device is fully operational from
2.7V to 5.5V and the clock/calendar portion of the
ISL12024IRTCZ device remains fully operational down to
1.8V (Standby Power Mode).
The ISL12024IRTCZ device provides 4k bits of EEPROM
with eight modes of BlockLock™ control. The BlockLock™
allows a safe, secure memory for critical user and
configuration data, while allowing a large user storage area.
Pin Descriptions
Serial Clock (SCL)
The SCL input is used to clock all data into and out of the
device. The input buffer on this pin is always active (not
gated). The pull-up resistor on this pin must use the same
voltage source as V_DD.
Serial Data (SDA)
SDA is a bidirectional pin used to transfer data into and out
of the device. It has an open drain output and may be wire
ORed with other open drain or open collector outputs. The
input buffer is always active (not gated).
This open drain output requires the use of a pull-up resistor.
The pull-up resistor on this pin must use the same voltage
source as V_DD. The output circuitry controls the fall time of the
output signal with the use of a slope controlled pull-down. The
circuit is designed to comply with 400kHz I²C interface speed.
V_BAT
This input provides a backup supply voltage to the device.
V_BAT supplies power to the device in the event the V_DD
supply fails. This pin can be connected to a battery, a Super
Cap or tied to ground if not used.
IRQ/F_OUT (Interrupt Output/Frequency Output)
This dual function pin can be used as an interrupt or
frequency output pin. The IRQ/F_OUT mode is selected via
the frequency out control bits of the INT register.
• Interrupt Mode. The pin provides an interrupt signal
output. This signal notifies a host processor that an alarm
has occurred and requests action. It is an open drain
active low output.
• Frequency Output Mode. The pin outputs a clock signal
which is related to the crystal frequency. The frequency
output is user selectable and enabled via the I²C bus. It is
an open drain output.
X1, X2
The X1 and X2 pins are the input and output, respectively, of
an inverting amplifier. An external 32.768kHz quartz crystal is
used with the ISL12024IRTCZ to supply a timebase for the
real-time clock. Internal compensation circuitry provides high
accuracy over the operating temperature range from -40°C to
+85°C. This oscillator compensation network can be used to
calibrate the crystal timing accuracy over-temperature either
during manufacturing, or with an external temperature sensor
and microcontroller for active compensation. The X2 pin is
intended to drive a crystal only, and should not drive any
external circuit.
X1
X2
FIGURE 7. RECOMMENDED CRYSTAL CONNECTION
Real-Time Clock Operation
The real-time clock (RTC) uses an external 32.768kHz quartz
crystal to maintain an accurate internal representation of the
second, minute, hour, day, date, month and year. The RTC
has leap-year correction. The clock also corrects for months
having fewer than 31 days and has a bit that controls 24 hour
or AM/PM format. When the ISL12024IRTCZ powers up after
the loss of both V_DD and V_BAT, the clock will not operate until
at least one byte is written to the clock register.
Reading the Real-Time Clock
The RTC is read by initiating a Read command and specifying
the address corresponding to the register of the real-time
clock. The RTC registers can then be read in a sequential
read mode. Since the clock runs continuously, and a read
7
FN6749.1
December 15, 2011