ISL12025 Datasheet, PDF (8/27 Pages) Intersil Corporation – Real-Time Clock/Calendar with I2C Bus and EEPROM

ISL12025
Description
The ISL12025 device is a Real-Time Clock with
clock/calendar, two polled alarms with integrated 512x8
EEPROM configured in 16 Bytes per page format, oscillator
compensation, CPU Supervisor (Power-on Reset, Low
Voltage Sensing and Watchdog Timer) 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. There is a repeat mode for the alarms allowing a
periodic interrupt.
The ISL12025 device integrates CPU Supervisory functions
(POR, WDT) and Battery Switch. There is Power-On-Reset
(RESET) output with 250ms delay from power-on. It will also
assert RESET when V_DD goes below the specified
threshold. The V_trip threshold is selectable via
VTS2/VTS1/VTS0 registers to five (5) preselected levels.
There is WatchDog Timer (WDT) with 3 selectable time-out
periods (0.25s, 0.75s and 1.75s) and disabled setting. The
WatchDog Timer activates the RESET pin when it expires.
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 ISL12025 device is fully operational from 2.7V to
5.5V and the clock/calendar portion of the ISL12025 device
remains fully operational down to 1.8V (Standby Power
Mode).
The ISL12025 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 for 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.
RESET
The RESET signal output can be used to notify a host
processor that the Watchdog timer has expired or the V_DD
voltage supply has dipped below the V_RESET threshold. It is
an open drain, active LOW output. Recommended value for
the pull-up resistor is 10kΩ. If unused, it can be tied to
ground.
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 ISL12025 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
(see Figure 11).
NOTE: NO EXTERNAL COMPENSATION RESISTORS OR
CAPACITORS ARE NEEDED OR ARE RECOMMENDED
TO BE CONNECTED TO THE X1 AND X2 PINS.
X1
X2
FIGURE 11. 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
8
FN6371.3
August 13, 2008