ISL12025 Intersil Corporation, ISL12025 Datasheet - Page 23

• Manufacturer Part Number: ISL12025
• Description: Real-Time Clock/Calendar
• Manufacturer: Intersil Corporation

to two weeks (with >1F). A simple silicon or Schottky barrier
diode can be used in series with V
supercapacitor, which is connected to the V
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
powered operations predictable. In Legacy modes, the V
pin can power the chip if the voltage is above V
V
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
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
I
is programmed for I
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
.
.
2
2
TRIP
C communications cease regardless of whether the device
C Communications During Battery Backup and
(X1227
switchover combined with I
MODE
Mode)
C
D
A
B
. This makes it possible to generate alarms and
TABLE 9. I
SBIB BIT
0
0
1
1
2
2
C operation in Battery Backup Mode.
C, LV RESET, AND BATTERY BACKUP OPERATION SUMMARY (Shaded Row is same as X1227 operation)
BSW
BIT
0
1
0
1
23
2
C operation in Battery Backup
DD
V
V
Standard Mode,
Standard Mode,
SWITCHOVER
Legacy Mode,
Legacy Mode,
TRIP
TRIP
goes below V
DD
V
V
VOLTAGE
DD
DD
VBAT
to charge the
= 2.2V typ
= 2.2V typ
< V
< V
BAT
BAT
BAT
DD
RESET
pin. Try to
and
I
V
2
BAT
C ACTIVE IN
YES, only if
DD
BACKUP?
BATTERY
, then
DD
>V
BAT
NO
NO
NO
RESET
ISL12025
EE PROM WRITE/READ
IN BATTERY BACKUP?
• Mode B - In this mode the selection bits indicate
• Mode C - In this mode the selection bits indicate a low
• Mode D - In this mode the selection bits indicate
2.7V TO 5.5V
Mode. In actuality the V
switching to battery backup, which will disable I
ANYTIME the device goes into Battery Backup Mode.
Regardless of the battery voltage, the I
to the V
switchover to battery backup at V
communications in battery backup. In order to
communicate in Battery Backup Mode, the V
voltage must be less than the V
must be greater than V
bus pins must go to V
the same as the normal operating mode of the X1227
device
V
battery backup. Operation is actually identical to Mode A
with I
communications (see Figure 28).
switchover to battery backup at V
communications in battery backup. This mode is unique in
that there is I
than V
the safest for guaranteeing I
when there is a Valid V
FIGURE 28. SUPERCAPACITOR CHARGING CIRCUIT
DD
YES
NO
NO
NO
switchover combined with no communications in
2
C communications down to V
RESET
RESET
2
or V
C communication as long as V
voltage (see Figure 29).
BAT
V
Operation of I
V
communications. Battery switchover at
V
Operation of I
Mode, but only for
V
Bus must have pullups to V
Operation of I
V
communications. Battery switchover at
V
Operation of I
V
DD
DD
TRIP
BAT
DD
TRIP
BAT
BAT
, whichever is greater. This mode is
V
DD
RESET
= V
= V
, whichever is higher.
DD
SS
.
> V
.
V
to communicate. This mode is
(see Figure 29).
RESET
RESET
will go below V
BAT
DD
2
C communications only
. Also, pull-ups on the I
> V
2
2
2
2
BAT
C bus down to
C bus into Battery Backup
C bus down to
C bus down to V
, then below that no
, then below that no
DD
DD
RESET
NOTES
DD
voltage AND V
<V
< V
2
= V
BAT
.
C will work down
BAT
SUPERCAPACITOR
RESET
RESET
, and I
BAT
, and no I
RESET
DD
October 18, 2006
.
2
RESET
C
is higher
2
, then no
before
C
DD
FN6371.1
2
2
C
or
C