ISL12026 Datasheet, PDF (7/24 Pages) Intersil Corporation – Real Time Clock/Calendar with EEPROM

ISL12026
Description
The ISL12026 device is a Real Time Clock with clock/
calendar, 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, 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 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 SuperCap.
The entire ISL12026 device is fully operational from 2.7 to
5.5V and the clock/calendar portion of the ISL12026 device
remains fully operational down to 1.8V (Standby Mode).
The ISL12026 device provides 4K bits of EEPROM with 8
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
SuperCap 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 ISL12026 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. X2 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 ISL12026 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 takes a finite amount of time, there is the
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FN8231.5
October 23, 2006