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21-0036

I2C Serial Real-Time Clock

Maxim Integrated 

DS1339 I2C Serial Real-Time Clock

Table 2. Crystal Specifications*

PARAMETER

Nominal Frequency

Series Resistance

Load Capacitance

SYMBOL MIN TYP MAX

fO

32.768

ESR

50

CL

6

UNITS

kHz

kΩ

pF

*The crystal, traces, and crystal input pins should be isolated from RF generating signals. Refer to

Application Note 58: Crystal Considerations for Dallas Real-Time Clocks for additional specifications.

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. Additional

error is added by crystal frequency drift caused by temperature shifts. External circuit noise coupled into the

oscillator circuit may result in the clock running fast. Figure 4 shows a typical PC board layout for isolating the

crystal and oscillator from noise. Refer to Application Note 58: Crystal Considerations with Dallas Real-Time

Clocks for detailed information

DS1339C ONLY

The DS1339C integrates a standard 32,768Hz crystal in the package. Typical accuracy at nominal VCC and +25°C

is approximately 10ppm. Refer to Application Note 58 for information about crystal accuracy vs. temperature.

Figure 4. Typical PC Board Layout for Crystal

LOCAL GROUND PLANE (LAYER 2)

X1

CRYSTAL

X2

NOTE: AVOID ROUTING SIGNALS IN

THE CROSSHATCHED AREA (UPPER

LEFT-HAND QUADRANT) OF THE

PACKAGE UNLESS THERE IS A

GROUND PLANE BETWEEN THE

SIGNAL LINE AND THE PACKAGE.

GND

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