PCF8523 NXP [NXP Semiconductors], PCF8523 Datasheet - Page 15

• Manufacturer Part Number: PCF8523
• Description: Real-Time Clock (RTC) and calendar
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
PCF8523
Product data sheet
8.5.2 Battery switch-over function
The PCF8523 has a backup battery switch-over circuit, which monitors the main power
supply V
condition is detected.
One of two operation modes can be selected:
V
Generation of interrupts from the battery switch-over is controlled via the BSIE bit (see
register Control_2). If BSIE is enabled, the INT1 follows the status of bit BLF (register
Control_3). Clearing BLF immediately clears INT1.
When a power failure condition occurs and the power supply switches to the battery the
following sequence occurs:
The battery switch flag BSF can be cleared by using the interface after the power supply
has switched to V
The interface is disabled in battery backup operation:
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.
th(sw)bat
•
•
•
•
Standard mode: the power failure condition happens when:
V
Direct switching mode: the power failure condition happens when V
Direct switching from V
Interface inputs are not recognized, preventing extraneous data being written to the
device.
Interface outputs are high-impedance.
DD
DD
< V
is the battery switch threshold voltage. Typical value is 2.5 V.
and automatically switches to the backup battery when a power failure
BAT
All information provided in this document is subject to legal disclaimers.
AND V
DD
. It must be cleared to clear the interrupt.
DD
Rev. 3 — 30 March 2011
< V
DD
th(sw)bat
to V
BAT
without requiring V
Real-Time Clock (RTC) and calendar
DD
to drop below V
PCF8523
© NXP B.V. 2011. All rights reserved.
DD
th(sw)bat
< V
BAT
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