Datasheet

PCF2127AT All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 6 — 11 July 2013 26 of 86
NXP Semiconductors
PCF2127AT
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
V
PFI
and 1.25 V:
• If V
PFI
> 1.25 V, PFO = HIGH (through the external pull-up resistor)
• If V
PFI
< 1.25 V, PFO = LOW
Fig 11. PFO signal behavior when battery switch-over is enabled in direct switching
mode and V
th(uvp)
< V
BAT
001aaj320
internal power supply (= V
BBS
)
comparator
enabled
comparator
disabled
comparator
enabled
V
th(sw)bat
(= 2.5 V)
V
th(uvp)
V
DD
V
BBS
V
BBS
V
BAT
PF0
t
rec
V
DD
(= 0 V)
Fig 12. PFO signal behavior when battery switch-over is disabled
001aaj321
comparator always enabled
V
th(sw)bat
(= 2.5 V)
V
DD
V
th(uvp)
PF0