ISL12020 Datasheet, PDF (7/25 Pages) Intersil Corporation – Low Power RTC with VDD Battery Backed SRAM and Embedded Temp Compensation ±5ppm with Auto Day Light Saving

ISL12020
EQUIVALENT AC OUTPUT LOAD CIRCUIT FOR V_DD = 5V
5.0V
SDA
AND
IRQ/FOUT
1533Ω
FOR V_OL= 0.4V
AND I_OL = 3mA
100pF
FIGURE 1. STANDARD OUTPUT LOAD FOR TESTING THE
DEVICE WITH V_DD = 5.0V
General Description
The ISL12020 devices are low power real time clocks
(RTCs) with embedded temperature sensors. They contain
crystal frequency compensation circuitry over the operating
temperature range, clock/calendar, power fail and low
battery monitors, brown out indicator with separate
(LVRSET) reset pin (ISL12021 only), 1 periodic or polled
alarm, intelligent battery backup switching and 128 Bytes of
battery-backed user SRAM.
The oscillator uses an external, low cost 32.768kHz crystal.
The real time clock tracks time with separate registers for
hours, minutes and seconds. The device has calendar
registers for date, month, year and day of the week. The
calendar is accurate through 2099, with automatic leap year
correction. In addition, both the ISL12020 could be
programmed for automatic Daylight Saving Time (DST)
adjustment by entering local DST information.
The ISL1202x’s alarm can be set to any clock/calendar value
for a match. For example, every minute, every Tuesday or at
5:23 AM on March 21. The alarm status is available by
checking the Status Register, or the device can be
configured to provide a hardware interrupt via the IRQ pin.
There is a repeat mode for the alarm allowing a periodic
interrupt every minute, every hour, every day, etc.
The device also offers a backup power input pin. This V_BAT
pin allows the device to be backed up by battery or Super
Cap with automatic switchover from V_DD to V_BAT. The
ISL12020 devices are specified for V_DD = 2.7V to 5.5V and
the clock/calendar portion of the device remains fully
operational in battery backup mode down to 1.8V (Standby
Mode). The V_BAT level is monitored and reported against
preselected levels. The first report is registered when the
V_BAT level falls below 85% of nominal level, the second level
is set for 75%. Battery levels are stored in V_BATM registers.
The ISL12020 offers a “Brown Out” alarm once the V_DD
falls below a pre-selected trip level. In the ISL12020, this
allows system Micro to save vital information to memory
before complete power loss. There are six V_DD levels that
could be selected for initiation of brown out alarm.
Pin Descriptions
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 device to supply a timebase for the real time
clock. Internal compensation circuitry with internal
temperature sensor provides frequency corrections for
selected popular crystals to ±5ppm over the operating
temperature range from -40°C to +85°C. (See “Application
Section” on page 22 for recommended crystal). ISL12020
allows the user to input via I2C serial bus the temperature
variation profile of crystals not listed in the “Application
Section” on page 22. This oscillator compensation network
can also be used to calibrate the initial crystal timing
accuracy at room temperature. The device can also be
driven directly from a 32.768kHz source at pin X1.
X1
X2
FIGURE 2. RECOMMENDED CRYSTAL CONNECTION
VBAT
This input provides a backup supply voltage to the device.
VBAT supplies power to the device in the event that the VDD
supply fails. This pin can be connected to a battery, a Super
Capacitor or tied to ground if not used. See the Battery
Monitor parameter in the DC Operating Characteristics-RTC
on page 3.
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 control/status 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.
Serial Clock (SCL)
The SCL input is used to clock all serial data into and out of
the device. The input buffer on this pin is always active (not
gated). It is disabled when the backup power supply on the
V_BAT pin is activated to minimize power consumption.
7
FN6450.0
March 29, 2007