PC8523-1 Просмотр технического описания (PDF) - NXP Semiconductors.

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PC8523-1

Real-Time Clock (RTC) and calendar

NXP Semiconductors. 

NXP Semiconductors

PCF8523

Real-Time Clock (RTC) and calendar

8.5.2 Battery switch-over function

The PCF8523 has a backup battery switch-over circuit. It monitors the main power supply

VDD 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:

VDD < VBAT AND VDD < Vth(sw)bat

• Direct switching mode: the power failure condition happens when VDD < VBAT.

Direct switching from VDD to VBAT without requiring VDD to drop below Vth(sw)bat

Vth(sw)bat is the battery switch threshold voltage. Typical value is 2.5 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:

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 VDD. 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

PCF8523

Product data sheet

All information provided in this document is subject to legal disclaimers.

Rev. 7 — 28 April 2015

© NXP Semiconductors N.V. 2015. All rights reserved.

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