PCF8564A datasheet(22/86 Pages) NXP

22 / 86 page

NXP Semiconductors

PCA2131

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

Battery switch-over function

mode

Conditions

Potential of

Voper(int) and

VBBS

VDD > VBAT OR VDD > Vth(sw)bat

VDD

standard

VDD < VBAT AND VDD < Vth(sw)bat

VBAT

VDD > VBAT

VDD

direct switching

VDD < VBAT

VBAT

disabled

only VDD available,

VBAT must be put to ground

VDD

Table 23. Output pin BBS

The output pin BBS can be used as a supply for external devices with battery backup

needs, such as SRAM (see [1]).

7.6 Oscillator stop detection function

The PCA2131 has an on-chip oscillator detection circuit which indicates the status of

the oscillation by monitoring the supply of oscillator: whenever the supply is out of the

expected range, a reset occurs and the oscillator stop flag OSF (in register Seconds) is

set logic 1.

• Power-on:

1. The oscillator is not running, the chip is in reset (OSF is logic 1).

2. When the oscillator starts running and supply is OK after power-on, the chip exits

from reset.

3. The flag OSF is still logic 1 and can be cleared (OSF set logic 0) by command.

• Power supply failure:

1. When the power supply of the chip drops below a certain value (Vlow), typically

1.2 V, the oscillator supply also fails and a reset occurs.

2. When the power supply returns to normal operation, the oscillator supply is OK

again, the chip exits from reset.

3. The flag OSF is still logic 1 and can be cleared (OSF set logic 0) by command.

4. When OSF flag is cleared an OTP refresh should be performed (see Section 7.3.2).

PCA2131

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

Product data sheet

Rev. 1.0 — 26 July 2021

22 / 86

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