ISL12020MIRZ-T7A Datasheet, PDF (11/34 Pages) Intersil Corporation – Low Power RTC with Battery Backed SRAM, Integrated ±5ppm Temperature Compensation and Auto Daylight Saving

ISL12020M
Typical Performance Curves Temperature is +25°C unless otherwise specified. (Continued)
110
100
80
60
62.5ppm
90
V_DD = 5.5V
40
80
V_DD = 3.3V
20
0
70
-20
60
V_BAT = 2.7V
-40
50
-60
32ppm
0ppm
-31ppm
-61.5ppm
40-40
-20
0
20
40
60
80
TEMPERATURE (°C)
-80-40
-20
0
20
40
60
80
TEMPERATURE (°C)
FIGURE 11. I_DD with TSE = 1 vs TEMPERATURE
FIGURE 12. OSCILLATOR CHANGE vs TEMPERATURE AT
DIFFERENT AGING SETTINGS (IATR) (BETA SET FOR
1ppm STEPS)
General Description
The ISL12020M device is a low power real time clock (RTC) with
embedded temperature sensor and crystal. It contains crystal
frequency compensation circuitry over the operating temperature
range good to ±5ppm accuracy. It also contains a clock/calendar
with Daylight Savings Time (DST) adjustment, 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 internal 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
ISL12020M could be programmed for automatic Daylight
Savings Time (DST) adjustment by entering local DST
information.
The ISL12020M’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 ISL12020M
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 ISL12020M 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.
Functional Description
Power Control Operation
The power control circuit accepts a V_DD and a V_BAT input. Many
types of batteries can be used with Intersil RTC products. For
example, 3.0V or 3.6V Lithium batteries are appropriate, and
battery sizes are available that can power the ISL12020M for up
to 10 years. Another option is to use a Super Capacitor for
applications where V_DD is interrupted for up to a month. See the
“Application Section” on page 28 for more information.
Normal Mode (V_DD) to Battery-Backup Mode
(V_BAT)
To transition from the V_DD to V_BAT mode, both of the following
conditions must be met:
Condition 1:
V_DD < V_BAT - V_BATHYS
where V_BATHYS  50mV
Condition 2:
V_DD < V_TRIP
where V_TRIP  2.2V
Battery-Backup Mode (V_BAT) to Normal Mode
(V_DD)
The ISL12020M device will switch from the V_BAT to V_DD mode
when one of the following conditions occurs:
Condition 1:
V_DD > V_BAT + V_BATHYS
where V_BATHYS 50mV
Condition 2:
V_DD > V_TRIP + V_TRIPHYS
where V_TRIPHYS  30mV
These power control situations are illustrated in Figures 13 and
14.
11
FN6667.5
December 13, 2011