PCF8564A datasheet(18/86 Pages) NXP

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NXP Semiconductors

PCA2131

Nano-power highly accurate RTC with integrated quartz crystal for automotive applications

PWRMNG[2:0]

Function

000

battery switch-over function is enabled in standard mode;

battery low detection function is enabled

001,010

battery switch-over function is enabled in standard mode;

battery low detection function is disabled

011

battery switch-over function is enabled in direct switching mode;

battery low detection function is enabled

100,101

battery switch-over function is enabled in direct switching mode;

battery low detection function is disabled

110,111

[1] [2] battery switch-over function is disabled, only one power supply

(VDD);

battery low detection function is disabled

Table 22. Power management control bit description

[1]

Default value.

[2]

When the battery switch-over function is disabled, the device works only with the power supply VDD. VBAT must be put to

ground and the battery low detection function is disabled.

7.5.1 Battery switch-over function

PCA2131 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

PCA2131

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

Product data sheet

Rev. 1.0 — 26 July 2021

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