PCF2127AT/1 NXP [NXP Semiconductors], PCF2127AT/1 Datasheet - Page 20

• Manufacturer Part Number: PCF2127AT/1
• Description: Integrated RTC, TCXO and quartz crystal
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
PCF2127A_2
Product data sheet
8.6.1.3 Battery switch-over disabled: only one power supply (V
8.6.1.4 Battery switch-over architecture
8.6.2 Battery backup supply
The direct switching mode is useful in systems where V
The direct switching mode is not recommended if the V
(e.g. V
reduced compared to the standard mode because the monitoring of V
not performed.
When the battery switch-over function is disabled:
The architecture of the battery switch-over circuit is shown in
The internal power supply (available on pin BBS) is equal to V
assured that there are decoupling capacitors on the pins V
The V
on the selected battery switch-over function mode:
Table 18.
The output pin BBS can be used as a supply for external devices with battery backup
needs, such as SRAM (see
driving capability when V
Battery switch-over function mode
standard
direct switching
disabled
Fig 6.
•
•
•
•
The power supply is applied on the V
The V
The internal power supply, available at the output pin BBS, is equal to V
The battery flag (BF) is always logic 0
BBS
DD
Battery switch-over circuit, simplified block diagram
= 3.3 V, V
voltage on the output pin BBS is equal to the internal power supply, depending
BAT
Output pin BBS
V
V
th(sw)bat
th(sw)bat
pin must be connected to ground
All information provided in this document is subject to legal disclaimers.
V
V
BAT
DD
BAT
comparators
≥ 3.0 V). In direct switching mode the power consumption is
Rev. 02 — 7 May 2010
BBS
V
V
CC
CC
Ref. 3
is driven from V
“AN10857”). For this case,
LOGIC
Conditions
V
V
V
V
V
only V
DD
DD
DD
DD
BAT
DD
logic
> V
< V
> V
< V
must be put to ground
pin
DD
DD
V
Integrated RTC, TCXO and quartz crystal
BAT
BAT
BAT
BAT
DD(int)
.
V
available,
V
BAT
DD
or V
and V
DD
DD
DD
DD
> V
switches
V
V
< V
DD(int)
DD(int)
is higher than V
and V
DD
th(sw)bat
DD
th(sw)bat
, V
Figure
Figure 7
DD
)
BAT
BAT
or V
(internal
power supply)
, and BBS.
PCF2127A
values are similar
6.
V
BAT
DD
BBS
001aag061
shows the typical
© NXP B.V. 2010. All rights reserved.
. It has to be
and V
BAT
V
V
V
V
V
V
DD
BBS
DD
BAT
DD
BAT
DD
at all times.
th(sw)bat
equals
20 of 80
is