pcf2127a NXP Semiconductors, pcf2127a Datasheet - Page 23

• Manufacturer Part Number: pcf2127a
• Description: Integrated Rtc, Tcxo And Quartz Crystal
• Manufacturer: NXP Semiconductors

NXP Semiconductors
PCF2127A_1
Product data sheet
8.6.4.1 Extra power fail detection when the battery switch over function is enabled
V
below the minimum operating voltage of the system, in order to allow the microcontroller
to perform early backup operations.
If the extra power fail detection function is not used, pin PFI must be connected to V
pin PFO must be left open circuit.
For illustration see
V
Fig 10. PFO signal behavior when battery switch-over is enabled in standard mode and
th(uvp)
•
•
th uvp
V
comparator
DD
enabled
(
V
(= 2.5 V)
When the power switches to the backup battery supply V
comparator is switched off and the power fail output at pin PFO goes (or remains)
LOW
When the power switches back to the main V
anymore and is pulled HIGH through the external pull-up resistance for a certain time
(t
th(sw)bat
V
(= 0 V)
rec
th(uvp)
V
)
V
PF0
value is usually set to a value that there are several milliseconds before V
BAT
DD
=
= 15.63 ms to 31.25 ms) and then the power fail comparator is enabled again
V
⎛
⎝
th(uvp)
R
----- -
R
1
2
+
> (V
1
⎞
⎠
Figure 10
V
×
BBS
BAT
1.25V
Rev. 01 — 21 January 2010
, V
th(sw)bat
and
)
internal power supply (= V
Figure
11.
Integrated RTC, TCXO and quartz crystal
comparator
disabled
DD
BBS
, the pin PFO is not driven LOW
)
t
rec
BAT
= [15.63 : 31.25] ms
, the power fail
V
BBS
PCF2127A
© NXP B.V. 2010. All rights reserved.
comparator
DD
enabled
001aaj319
SS
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falls
and
(1)