pcf2127a NXP Semiconductors, pcf2127a Datasheet - Page 22

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

NXP Semiconductors
PCF2127A_1
Product data sheet
8.6.4 Extra power fail detection function
The PCF2127A has an extra power fail detection circuit which compares the voltage at the
power fail input pin (PFI) to an internal reference voltage equal to 1.25 V.
If V
LOW output which requires an external pull-up resistor in any application.
The extra power fail detection function is typically used as a low voltage detection for the
main power supply V
Usually R1 and R2 should be chosen such that the voltage at pin PFI
Fig 8.
Fig 9.
•
•
V
DD
V
PFI
is higher than 1.25 V at start-up
falls below 1.25 V when V
by
(= 2.5 V)
th(bat)low
= V
< 1.25 V the power fail output PFO is driven LOW. PFO is an open-drain, active
V
Equation
BLF
BBS
INT
BAT
Battery low detection behavior with bit BLIE logic 1 (enabled)
Typical application of the extra power fail detection function
1:
DD
Rev. 01 — 21 January 2010
(see
Figure
DD
PCF2127A
falls below a desired threshold voltage, V
(internal)
9).
1.25 V
internal power supply (= V
15
14
PFI
PFO
Integrated RTC, TCXO and quartz crystal
V
V
DD
V
SS
BAT
R1
R2
001aaj678
R PU
BBS
)
PCF2127A
© NXP B.V. 2010. All rights reserved.
th(uvp)
, defined
001aaj322
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