ISL12023 Datasheet, PDF (8/28 Pages) Intersil Corporation – Low Power RTC with Battery-Backed SRAM and Embedded Temp Compensation ±5ppm with Auto Daylight Saving

ISL12023
Typical Performance Curves Temperature is +25°C unless otherwise specified. (Continued)
110
100
90
V_DD = 5.5V
80
V_BAT = 2.7V
70
60
V_DD = 3.3V
50
40
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
FIGURE 8. I_DD WITH TSE = 1 vs TEMPERATURE
110
100
90
80
V_BAT = 5.5V
70
60
V_BAT = 3.0V
50
V_BAT = 1.8V
40
30
20 _-40
-20
0
20
40
60
80
TEMPERATURE (°C)
FIGURE 9. I_BAT with TSE = 1, BTSE = 1 vs TEMPERATURE
General Description
The ISL12023 device is a low power real time clock (RTC) with
embedded temperature sensors. It contains crystal frequency
compensation circuitry over the operating temperature range,
clock/calendar, power fail and low battery monitors, brownout
indicator with separate low voltage reset pin (LVRST),
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, the ISL12023 could be programmed
for automatic Daylight Savings Time (DST) adjustment by
entering local DST information.
The ISL12023’s alarm can be set to any clock/calendar
value for a match. For example, every minute, every
Tuesday or at 5:23 a.m. 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
capacitor with automatic switchover from V_DD to V_BAT. The
ISL12023 device is 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 PWR_VBAT registers.
The ISL12023 offers a “Brownout” alarm once the V_DD falls
below a pre-selected trip level. 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 the Brownout 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 24 for recommended crystal). The
ISL12023 allows the user to input via I²C serial bus the
temperature variation profile of an individual crystal. The
oscillator compensation network can also be used to
calibrate the initial crystal timing accuracy to less than 1ppm
error at room temperature. The device can also be driven
directly from a 32.768kHz source at pin X1.
X1
X2
FIGURE 10. RECOMMENDED CRYSTAL CONNECTION
V_BAT
This input provides a backup supply voltage to the device.
V_BAT supplies power to the device in the event that the V_DD
supply fails. The device will automatically switch to the V_BAT
input when V_DD drops below a prescribed level. See the
Battery Monitor parameter in the electrical spec table titled
“DC Operating Characteristics-RTC” on page 3. This pin can
be connected to a battery, a super capacitor or tied to ground
if not used.
8
FN6682.2
June 24, 2009