ISL12028 Datasheet, PDF (16/28 Pages) Intersil Corporation – Real Time Clock/Calendar with EEPROM

ISL12028
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”. A description of power switchover follows
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)
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 back up
and unless the battery is disconnected or the voltage
decreases, the device will no longer operate from V_DD.
To select the 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:
V_DD > V_BAT +V_BATHYS
The Legacy Mode power control conditions are illustrated in
Figure 15.
V_BAT
V_DD
Off
VOLTAGE
On
In
FIGURE 15. BATTERY SWITCHOVER IN LEGACY MODE
16
FN8233.5
October 18, 2006