PCF2127 View Datasheet(PDF) - NXP Semiconductors.
Part Name
Description
MFG CO.
'PCF2127' PDF : 101 Pages View PDF
NXP Semiconductors
PCF2127
Accurate RTC with integrated quartz crystal for industrial applications
Usually R1 and R2 should be chosen such that the voltage at pin PFI
• is higher than 1.25 V at start-up
• falls below 1.25 V when VDD falls below a desired threshold voltage, Vth(uvp), defined
by Equation 1:
Vthuvp
=
R----1-
R2
+
1
1.25V
(1)
Vth(uvp) value is usually set to a value that there are several milliseconds before VDD falls
below the minimum operating voltage of the system, in order to allow the microcontroller
to perform early backup operations, like terminating the communication with the
PCF2127.
The value of C is determined from Equation 2:
C
=
---R---0-1--./-0-/--R2----2---
A-----s
V
(2)
If the extra power fail detection function is not used, pin PFI must be connected to VSS and
pin PFO must be left open circuit.
8.6.3.1 Extra power fail detection when the battery switch-over function is enabled
• When the power switches to the backup battery supply VBAT, the power fail
comparator is switched off and the power fail output at pin PFO goes (or remains)
LOW
• When the power switches back to the main VDD, the pin PFO is not driven LOW
anymore. It is pulled HIGH through the external pull-up resistance for a certain time
(trec = 15.63 ms to 31.25 ms). Then the power fail comparator is enabled again
For illustration, see Figure 11 and Figure 12.
PCF2127
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 8 — 19 December 2014
© NXP Semiconductors N.V. 2014. All rights reserved.
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