ISL12028_10 Datasheet, PDF (16/29 Pages) Intersil Corporation – Real Time Clock/Calendar with I2C Bus™ and EEPROM

ISL12028, ISL12028A
for up to a month. See “Application Section” on page 22 for
more information.
There are two options for setting the change-over conditions
from V_DD to Battery back-up mode. The BSW bit in the PWR
register controls this operation.
Option 1 - Standard Mode (Default for ISL12028A)
Option 2 - Legacy Mode (Default for ISL12028)
TABLE 7. V_BAT TRIP POINT WITH DIFFERENT BSW SETTING
V_BAT TRIP POINT
BSW BIT
(V)
POWER CONTROL SETTING
0
2.2
Standard Mode (ISL12028A)
1
V_DD < V_BAT
Legacy Mode (ISL12028)
Note that applications that have V_BAT > V_DD will require the
ISL12028A (standard mode) for proper start-up. Note that
the I²C may or may not be operational during battery
backup, that function is controlled by the SBIB bit. That
operation is covered after the power control section.
OPTION 1 - STANDARD POWER CONTROL MODE
(DEFAULT FOR ISL12028A)
In the Standard mode, the supply will switch over to the
battery when V_DD drops below V_TRIP or V_BAT, whichever is
lower. In this mode, accidental operation from the battery is
prevented since the battery backup input will only be used
when the V_DD supply is shut off.
To select Option 1, BSW bit in the Power Register must be
set to “BSW = 0”. Following is a description of power
switchover.
Standard Mode Power Switchover
• Normal Operating 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 ISL12028 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
There are two discrete situations that are possible when
using Standard Mode: V_BAT < V_TRIP and V_BAT > V_TRIP.
These two power control situations are illustrated in
Figures 13 and 14.
BATTERY
BACKUP
V_DD
MODE
V_TRIP
V_BAT
2.2V
1.8V
V_BAT - V_BATHYS
V_BAT + V_BATHYS
FIGURE 13. BATTERY SWITCHOVER WHEN V_BAT < V_TRIP
V_DD
V_BAT
V_TRIP
V_TRIP
BATTERY BACKUP
MODE
3.0V
2.2V
V_TRIP + V_TRIPHYS
FIGURE 14. BATTERY SWITCHOVER WHEN V_BAT > V_TRIP
OPTION 2 - LEGACY POWER CONTROL MODE
(DEFAULT FOR ISL12028)
The Legacy Mode follows conditions set in X1226 products.
In this mode, switching from V_DD to V_BAT is simply done by
comparing the voltages and the device operates from
whichever is the higher voltage. Care should be taken when
changing from Normal to Legacy Mode. If the V_BAT voltage is
higher than V_DD, then the device will enter battery backup and
unless the battery is disconnected or the voltage decreases,
the device will no longer operate from V_DD. If that is the
situation on initial power-up, then I²C communication may not
be possible. For these applications, the ISL12028A should be
used.
To select Option 2, BSW bit in the Power Register must be
set to “BSW = 1”
• Normal Mode (V_DD) to Battery Backup Mode (V_BAT)
To transition from the V_DD to V_BAT mode, the following
conditions must be met:
V_DD < V_BAT - V_BATHYS
• Battery Backup Mode (V_BAT) to Normal Mode (V_DD)
The device will switch from the V_BAT to V_DD mode when the
following condition occurs:
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FN8233.8
August 9, 2010