DS1339 I

9 of 18

Table 1. Crystal Specifications*

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

Nominal Frequency

32.768

kHz

Series Resistance

ESR

45

k

W

Load Capacitance

6

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.

Figure 4. Oscillator Circuit Showing Internal Bias Network

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 5 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

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

Figure 5. Typical PC Board Layout for Crystal

COUNTDOWN

CHAIN

RTC

REGISTERS

RTC

X1

X2

CRYSTAL

C

C

LOCAL GROUND PLANE (LAYER 2)

CRYSTAL

X1

X2

GND

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.