ISL12029 Intersil Corporation, ISL12029 Datasheet - Page 24

• Manufacturer Part Number: ISL12029
• Description: Real Time Clock/Calendar
• Manufacturer: Intersil Corporation

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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
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
connected to the V
very low leakages, <1µA desireable. 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 operationis predicatable. In Legacy modes the
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. In this case if alarms are used
in backup mode, the IRQ/F
connected to V
the default mode is the Sandard mode.
BAT
TRIP
2.7-5.5V
FIGURE 28. SUPERCAPACITOR CHARGING CIRCUIT
pin can power the chip if the voltage is above V
. This makes it possible to generate alarms and
DD
BAT
to charge the supercapacitor, which is
V
BAT
voltage source. During initial power-up
CC
DD
pin. Try to use Schottky diodes with
V
may disappear intermittently for short
SS
OUT
V
24
back
pull up resistor must be
Supercapacitor
DD
DD
and
ISL12029
I
LVR Operation
Operation in Battery Backup mode and LVR is affected by
the BSW and SBIB bits as described earlier. 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 VDD goes below VRESET, then
I
is programmed for I
Table 10 describes 4 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 VDD
• 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
2
C communications cease regardless of whether the device
C Communications During Battery Backup and
switchover combined with I
mode. In actuality the VDD will go below 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
must be less than the VBAT voltage AND V
greater than V
must go to V
as the normal operating mode of the X1228 device
VDD switchover combined with no communications in
battery backup. Operation is actually identical to Mode A
with I
communications (see Figure 29).
switchover to battery backup at V
communications in battery backup. This mode is unique in
that there is I
than VRESET or VBAT, whichever is greater. This mode is
the safest for guaranteeing I
there is a Valid V
2
C communications down to V
RESET
BAT
2
C communication as long as VDD is higher
RESET
voltage (See Figure 29).
to communicate. This mode is the same
DD
2
C operation in battery backup mode.
. (see Figure 30)
. Also, pullups on the I
2
2
C operation in battery backup
C communications only when
DD
DD
DD
<V
<V
2
= V
BAT
BAT
C will work down
RESET
, and I
, and no I
RESET
2
DD
RESET
C bus pins
must be
2
C
, then no
April 17, 2006
2
C
before
voltage
FN6206.4
2
C