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 21 of 86
NXP Semiconductors
PCF2127AT
Integrated RTC, TCXO and quartz crystal
8.6.1.2 Direct switching mode
If V
DD
> V
BAT,
the internal power supply is V
DD
.
If V
DD
< V
BAT
, the internal power supply is V
BAT
.
The direct switching mode is useful in systems where V
DD
is higher than V
BAT
at all times.
This mode is not recommended if the V
DD
and V
BAT
values are similar (for example,
V
DD
= 3.3 V, V
BAT
 3.0 V). In direct switching mode, the power consumption is reduced
compared to the standard mode because the monitoring of V
DD
and V
th(sw)bat
is not
performed.
8.6.1.3 Battery switch-over disabled: only one power supply (V
DD
)
When the battery switch-over function is disabled:
• The power supply is applied on the V
DD
pin
• The V
BAT
pin must be connected to ground
• The internal power supply, available at the output pin BBS, is equal to V
DD
• The battery flag (BF) is always logic 0
Fig 5. Battery switch-over behavior in direct switching mode with bit BIE set logic 1
(enabled)
001aaj312
internal power supply (= V
BBS
)
cleared via interface
backup battery operation
BF
V
th(sw)bat
(= 2.5 V)
V
DD
(= 0 V)
V
BAT
V
DD
V
BBS
V
BBS
INT