PCF2131 datasheet(18/85 Pages) NXP

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NXP Semiconductors

PCF2131

Nano-power highly accurate RTC with integrated quartz crystal

7.5.1 Battery switch-over function

PCF2131 has a backup battery switch-over circuit which monitors the main power supply VDD. When a power

failure condition is detected, it automatically switches to the backup battery.

One of two operation modes can be selected:

Standard mode - the power failure condition happens when:

VDD < VBAT AND VDD < Vth(sw)bat

Vth(sw)bat is the battery switch threshold voltage. Typical value is 2.5 V. The battery switch-over in standard mode

works only for VDD > 2.5 V. Applying back-up battery voltage to VBAT without applying VDD supply will not power

on the device; only when VDD main power is supplied the device will start operating.

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

When a power failure condition occurs and the power supply switches to the battery, the following sequence

occurs:

1. The battery switch flag BF (register Control_3) is set to logic 1.

2. An interrupt is generated if the control bit BIE (register Control_3) is enabled (see Section 7.13.6).

3. If the control bit BTSE (register Control_3) is logic 1, the timestamp 4 registers store the time and date when

the battery switch occurred (see Section 7.12.4).

4. The battery switch flag BF is cleared by command; it must be cleared to clear the interrupt.

The interface and CLKOUT output are disabled in battery backup operation:

• Interface inputs are not recognized, preventing extraneous data being written to the device

• Interface outputs are high-impedance

For further information about I2C-bus communication and battery backup operation, see Section 7.16.3.

7.5.1.1 Standard mode

If VDD > VBAT OR VDD > Vth(sw)bat: Voper(int) is at VDD potential.

If VDD < VBAT AND VDD < Vth(sw)bat: Voper(int) is at VBAT potential.

PCF2131

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

Product data sheet

Rev. 2.0 — 5 October 2023

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PCF2131 датащи(PDF) 18 Page - NXP Semiconductors