RV-3049 datasheet(37/65 Pages) MICROCRYSTAL

37 / 65 page

Micro Crystal

DTCXO Temperature Compensated Real Time Clock / Calendar Module

RV-3049

37/65

5. COMPENSATION OF FREQUENCY DEVIATION AND FREQUENCY DRIFT vs

TEMPERATURE

There is a Thermometer and a Frequency Compensation Unit “FCU” built-in the RV-3049.

Based on all known tolerances and the measured ambient temperature, this Frequency Compensation Unit “FCU”

is calculating every 32 seconds a Frequency Compensation Value. The frequency compensation itself is achieved

by adding or subtracting clock-pulses to the 32.768 kHz reference clock, one compensation period takes 32

seconds.

All required parameters for frequency compensation are factory calibrated and should not be modified to profit from

best time accuracy.

Frequency deviations affecting the time accuracy of Real Time Clocks:

XTAL offset:

Xtal’s frequency deviation ±20 ppm @ 25°C

XTAL T0:

Xtal’s turnover temperature 25°C ±5°C

XTAL temp. coefficient:

Xtal’s frequency drift vs temperature -0.035 ppm * (T-T0)

2 ±10%

5.1. TEMPERATURE CHARACTERISTICS TUNING FORK CRYSTAL

Typical Frequency Deviation of a 32.768 kHz Tuning Fork Crystal over Temperature

-180.0

-160.0

-140.0

-120.0

-100.0

-80.0

-60.0

-40.0

-20.0

0.0

20.0

-60

-40

-20

100

T [°C]

-0.035 ppm * (T-T0)

2 (±10%)

T0 = 25°C (±5)

Above graph shows the typical frequency-deviation of a 32.768kHz “Tuning-Fork” Crystal over temperature.

The parabolic curve is specified in terms of turnover temperature “T0” and the quadratic thermal coefficient “β”.

T0: turnover temperature 25°C ±5°C

: 2

nd order temperature coefficient -0.035 ppm * (T-T

2 ±10% (quadratic thermal coefficient)

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