PCF2129 datasheet(16/86 Pages) PHILIPS

16 / 86 page

PCF2129

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Product data sheet

Rev. 7 — 19 December 2014

16 of 86

NXP Semiconductors

PCF2129

Accurate RTC with integrated quartz crystal for industrial applications

8.5 Power management functions

The PCF2129 has two power supplies:

VDD — the main power supply

VBAT — the battery backup supply

Internally, the PCF2129 is operating with the internal operating voltage Voper(int) which is

also available as VBBS on the battery backed output voltage pin, BBS. Depending on the

condition of the main power supply and the selected power management function,

Voper(int) is either on the potential of VDD or VBAT (see Section 8.5.3).

Two power management functions are implemented:

Battery switch-over function — monitoring the main power supply VDD and switching to

VBAT in case a power fail condition is detected (see Section 8.5.1).

Battery low detection function — monitoring the status of the battery, VBAT (see

Section 8.5.2).

The power management functions are controlled by the control bits PWRMNG[2:0] (see

Table 19) in register Control_3 (see Table 11):

[1]

Default value.

[2]

When the battery switch-over function is disabled, the PCF2129 works only with the power supply VDD.

VBAT must be put to ground and the battery low detection function is disabled.

Table 19.

Power management control bit description

PWRMNG[2:0]

Function

000

[1] battery switch-over function is enabled in standard mode;

battery low detection function is enabled

001

battery switch-over function is enabled in standard mode;