Datasheet

PCF2129 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
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 V
BBS
voltage on the output pin BBS is at the same potential as the internal operating
voltage V
oper(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 V
BBS
is driven from V
DD
.
Fig 9. Battery low detection behavior with bit BLIE set logic 1 (enabled)
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Table 20. Output pin BBS
Battery switch-over function
mode
Conditions Potential of
V
oper(int)
and
V
BBS
standard V
DD
> V
BAT
OR V
DD
> V
th(sw)bat
V
DD
V
DD
< V
BAT
AND V
DD
< V
th(sw)bat
V
BAT
direct switching V
DD
> V
BAT
V
DD
V
DD
< V
BAT
V
BAT
disabled only V
DD
available,
V
BAT
must be put to ground
V
DD