ISL12022 Datasheet, PDF (8/28 Pages) Intersil Corporation – Real Time Clock with On Chip ±5ppm Temp Compensation

ISL12022
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 ISL12022 device is a low power real time clock (RTCs)
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, 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 ISL12022 can be programmed for
automatic Daylight Savings Time (DST) adjustment by
entering local DST information.
The ISL12022’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/F_OUT
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
ISL12022 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 ISL12022 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 25 for recommended crystal). The
ISL12022 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. Device power will automatically switch to the
V_BAT input when V_DD drops below the switchover trip level
(V_TRIP). This pin can be connected to a battery, a super
capacitor 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 control/status register. It
is an open drain output.
8
FN6659.2
June 23, 2009