PT7C4339 Datasheet, PDF (5/22 Pages) Pericom Semiconductor Corporation – Real-time Clock Module

PT7C4339/4339C
Real-time Clock Module
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Functional Block Diagram
V_CC
Power Failure Detect
V_BACKUP
X1
32.768
kHz
X2
“C” version only
Trickle Charger Control
C_D
OSC
C_G
Counter Chain
Control Register
SQW/INT
Interrupt Control
Square Wave Output Control
Comparator 1
Comparator 2
Alarm 1 Register
(Sec, Min, Hour, Day/Date)
Alarm 2 Register
(Min, Hour, Day/Date)
Time Counter
(Sec,Min,Hour,Day,Date,Month,Year)
Address
Decoder
Address
Register
Shift Register
I /O
Interface
(I²C)
SCL
SDA
Oscillator Circuit
PT7C4339
The PT7C4339 uses an external 32.768 kHz crystal. Table1 specifies several crystal parameters for the external crystal. The
Block Diagram shows a functional schematic of the oscillator circuit. The startup time is usually less than 1 second when using a
crystal with the specified characteristics.
Table1 Crystal Specifications
Parameter
Symbol
Min
Typ
Max
Unit
Nominal Frequency
f_O
-
32.768
-
kHz
Series Resistance
ESR
-
-
70
k
Load Capacitance
C_L
-
6
-
pF
Note: The crystal, traces, and crystal input pins should be isolated from RF generating signals.
Clock Accuracy
The accuracy of the clock is dependent upon the accuracy of the crystal and the accuracy of the match between the capacitive
load of the oscillator circuit and the capacitive load for which the crystal was trimmed. Crystal frequency drift caused by
temperature shifts creates additional error. External circuit noise coupled into the oscillator circuit can result in the clock running
fast. Figure 2 shows a typical PC board layout for isolating the crystal and oscillator from noise.
PT7C4339C
The PT7C4339C integrates a standard 32,768Hz crystal in the package. Typical accuracy at nominal VCC and +25°C is
approximately ±10ppm.
2015-08-0008
PT0508-1 08/24/15
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