PCF2129 datasheet(21/86 Pages) PHILIPS

21 / 86 page

PCF2129

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Product data sheet

Rev. 7 — 19 December 2014

21 of 86

NXP Semiconductors

PCF2129

Accurate RTC with integrated quartz crystal for industrial applications

8.5.3 Battery backup supply

The VBBS voltage on the output pin BBS is at the same potential as the internal operating

voltage Voper(int), depending on the selected battery switch-over function mode:

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

needs, such as SRAM (see Ref. 3 “AN11186”). For this case, Figure 10 shows the typical

driving capability when VBBS is driven from VDD.

Fig 9.

Battery low detection behavior with bit BLIE set logic 1 (enabled)

Table 20.

Output pin BBS

Battery switch-over function

mode

Conditions

Potential of

Voper(int) and

VBBS

standard

VDD > VBAT OR VDD > Vth(sw)bat

VDD

VDD < VBAT AND VDD < Vth(sw)bat

VBAT

direct switching

VDD > VBAT

VDD

VDD < VBAT

VBAT

disabled

only VDD available,

VBAT must be put to ground

VDD

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