PCF2127ATSLASH1 datasheet(24/80 Pages) NXP

24 / 80 page

PCF2127A_2

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Product data sheet

Rev. 02 — 7 May 2010

24 of 80

NXP Semiconductors

PCF2127A

Integrated RTC, TCXO and quartz crystal

8.6.4.2

Extra power fail detection when the battery switch-over function is disabled

If the battery switch-over function is disabled and the power fail comparator is enabled,

the power fail output at pin PFO depends only on the result of the comparison between

VPFI and 1.25 V:

• If VPFI > 1.25 V, PFO = HIGH (through the external pull-up resistor)

• If VPFI < 1.25 V, PFO = LOW

Fig 11. PFO signal behavior when battery switch-over is enabled in direct switching

mode and Vth(uvp) < VBAT

001aaj320

internal power supply (= VBBS)

comparator

enabled

comparator

disabled

comparator

enabled

Vth(sw)bat

(= 2.5 V)

Vth(uvp)

VDD

VBBS

VBAT

PF0

trec

VDD (= 0 V)

Fig 12. PFO signal behavior when battery switch-over is disabled

001aaj321

comparator always enabled

Vth(sw)bat

(= 2.5 V)

VDD

Vth(uvp)

PF0

PCF2127AT/1 Datasheet(PDF) 24 Page - NXP Semiconductors

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