參數(shù)資料
型號(hào)： ISL12025
廠商： Intersil Corporation
英文描述： Real-Time Clock/Calendar with EEPROM(EEPROM實(shí)時(shí)時(shí)鐘/日歷)
中文描述： 實(shí)時(shí)時(shí)鐘/日歷（EEPROM的實(shí)時(shí)時(shí)鐘/日歷帶有EEPROM）
文件頁數(shù)： 23/27頁
文件大小： 412K
代理商： ISL12025
23
FN6371.2
October 19, 2007
minute. Using the pulse interrupt mode setting, the once-per-
minute interrupt functions as an indication of proper
oscillation.
Backup Battery Operation
Many types of batteries can be used with the Intersil RTC
products. 3.0V or 3.6V Lithium batteries are appropriate, and
sizes are available that can power a Intersil RTC device for
up to 10 years. Another option is to use a supercapacitor for
applications where V
DD
may disappear intermittently for
short periods of time. Depending on the value of
supercapacitor used, backup time can last from a few days
to two weeks (with >1F). A simple silicon or Schottky barrier
diode can be used in series with V
DD
to charge the
supercapacitor, which is connected to the V
BAT
pin. Try to
use Schottky diodes with very low leakages, <1μA
desirable.
Do not use the diode to charge a battery (especially lithium
batteries!)
There are two possible modes for battery backup operation;
Standard and Legacy Mode. In Standard Mode, there are no
operational concerns when switching over to battery backup
since all other devices functions are disabled. Battery drain
is minimal in Standard Mode and return to Normal V
DD
powered operations predictable. In Legacy modes, the V
BAT
pin can power the chip if the voltage is above V
DD
and
V
TRIP
.
This makes it possible to generate alarms and
communicate with the device under battery backup, but the
supply current drain is much higher than the Standard Mode
and backup time is reduced. During initial power-up, the
default mode is the Legacy Mode.
I
2
C Communications During Battery Backup and
LVR Operation
Operation in Battery Backup Mode and LVR is affected by
the BSW and SBIB bits as described previously. These bits
allow flexible operation of the serial bus and EEPROM in
Battery Backup Mode, but certain operational details need to
be clear before utilizing the different modes. The most
significant detail is that once V
DD
goes below V
RESET
, then
I
2
C communications cease regardless of whether the device
is programmed for I
2
C operation in Battery Backup Mode.
Table 9 describes four different modes possible with using
the BSW and SBIB bits and how they are affect LVR and
battery backup operation.
Mode A - In this mode selection bits indicate a low V
DD
switchover combined with I
2
C operation in Battery Backup
Mode. In actuality the V
DD
will go below V
RES2
before
switching to battery backup, which will disable I
C
ANYTIME the device goes into Battery Backup Mode.
Regardless of the battery voltage, the I
2
C will work down
to the V
RESET
voltage (see Figure 29).
Mode B - In this mode the selection bits indicate
switchover to battery backup at V
DD
<V
BAT
, and I
2
C
communications in battery backup. In order to
communicate in Battery Backup Mode, the V
RESET
voltage must be less than the V
BAT
voltage AND V
DD
must be greater than V
RESET
. Also, pull-ups on the I
2
C
bus pins must go to V
BAT
to communicate. This mode is
the same as the normal operating mode of the X1227
device
Mode C - In this mode the selection bits indicate a low
V
DD
switchover combined with no communications in
battery backup. Operation is actually identical to Mode A
with I
2
C communications down to V
DD
= V
RESET
, then no
communications (see Figure 28).
Mode D - In this mode the selection bits indicate
switchover to battery backup at V
DD
< V
BAT
, and no I
2
C
communications in battery backup. This mode is unique in
that there is I
2
C communication as long as V
DD
is higher
than V
RESET
or V
BAT
, whichever is greater. This mode is
the safest for guaranteeing I
2
C communications only
when there is a Valid V
DD
(see Figure 29).
.
FIGURE 28. SUPERCAPACITOR CHARGING CIRCUIT
V
DD
V
BAT
V
SS
SUPERCAPACITOR
2.7V TO 5.5V
TABLE 9. I
2
C, LV RESET, AND BATTERY BACKUP OPERATION SUMMARY
(Shaded Row is same as X1227 operation)
MODE
SBIB BIT
BSW
BIT
VBAT
SWITCHOVER
VOLTAGE
I
2
C ACTIVE IN
BATTERY
BACKUP
EE PROM WRITE/READ
IN BATTERY BACKUP
NOTES
A
0
0
Standard Mode,
V
TRIP
= 2.2V typ
NO
NO
Operation of I
2
C bus down to
V
DD
= V
RESET
, then below that no
communications. Battery switchover at
V
TRIP
.
Operation of I
2
C bus into Battery Backup
Mode, but only for
V
BAT
> V
DD
> V
RESET
.
Bus must have pull-ups to V
BAT
.
B
(X1227
Mode)
0
1
Legacy Mode,
V
DD
< V
BAT
YES, only if
V
BAT
> V
RESET
YES
ISL12025
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