PT7C4337_13 Datasheet, PDF (7/23 Pages) Pericom Semiconductor Corporation – Real-time Clock Module

PT7C4337
Real-time Clock Module (I²C Bus)
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Function Block
PT7C4337
X1
32.768
kHz
X2
C_{G OSC}
C_D
Counter Chain
Control Register
INTA
SQW/INTB
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
PT7C4337
The PT7C4337 uses an external 32.768 kHz crystal. Table2 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.
Table2 Crystal Specifications
Parameter
Symbol
Min
Typ
Max
Unit
Nominal Frequency
f_O
-
32.768
-
kHz
Series Resistance
ESR
-
-
70
k
Load Capacitance
C_L
-
6/12.5
-
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 1 shows a typical PC board layout for isolating the crystal and oscillator from noise.
2013-06-0002
PT0205-9 06/18/13
7