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2013-06-0002

PT0205-9

06/18/13

7

PT7C4337

Real-time Clock Module (I

Function Block

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

-

32.768

-

kHz

Series Resistance

ESR

-

-

70

k

Load Capacitance

-

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.

Time Counter

(Sec,Min,Hour,Day,Date,Month,Year)

Interrupt Control

Square Wave Output Control

Comparator 1

Alarm 2 Register

(Min, Hour, Day/Date)

Comparator 2

Alarm 1 Register

(Sec, Min, Hour, Day/Date)

Shift Register

Address

Decoder

Address

Register

INTA

SQW/INTB

SCL

SDA

PT7C4337

OSC

X1

X2

C

G

C

D

32.768

kHz

Control Register

Counter Chain

I /O

Interface