RV-8523 Datasheet, PDF (24/57 Pages) MICORO CRYSTAL SWITZERLAND – Real Time Clock

Micro Crystal
Real Time Clock / Calendar Module
RV-8523
9.2.2.BATTERY SWITCHOVER
The RV-8523 has a backup battery switchover circuit. It monitors the main power supply V_DD and switches
automatically to the backup battery when a power failure condition is detected.
One of two operation modes can be selected:
• Standard mode: the power failure condition happens when: V_DD < V_BAT AND V_DD < V_th(sw)bat
• Direct switching mode: the power failure condition happens when V_DD < V_BAT.
Direct switching from V_DD to V_BAT without requiring V_DD to drop below V_th(sw)bat
V_th(sw)bat is the battery switch threshold voltage. Typical value is 2.5 V.
Generation of interrupts from the battery switchover is controlled via the BSIE bit (register Control 2). If BSIE is
enabled, the INT_1 follows the status of bit BLF (register Control 3). Clearing BLF immediately clears INT_1.
When a power failure condition occurs and the power supply switches to the battery, the following sequence
occurs:
1. The battery switch flag BSF (register Control 3) is set logic 1
2. An interrupt is generated if the control bit BSIE (register Control 3) is enabled
The battery switch flag BSF can be cleared by using the interface after the power supply has switched to V_DD. It
must be cleared to clear the interrupt.
The interface is disabled in battery backup operation:
• Interface inputs are not recognized, preventing extraneous data being written to the device
• Interface outputs are high-impedance
Standard mode:
If V_DD > V_BAT OR V_DD > V_th(sw)bat the internal power supply is V_DD.
If V_DD < V_BAT AND V_DD < V_th(sw)bat the internal power supply is V_BAT.
Battery switchover behavior in standard mode and with bit BSIE set logic 1 (enabled):
24/57