RV-3029 Datasheet, PDF (37/67 Pages) MICORO CRYSTAL SWITZERLAND – DTCXO Temperature Compensated Real Time Clock

Micro Crystal
DTCXO Temperature Compensated Real Time Clock / Calendar Module
RV-3029
5. COMPENSATION OF FREQUENCY DEVIATION AND FREQUENCY DRIFT vs
TEMPERATURE
There is a Thermometer and a Frequency Compensation Unit “FCU” built-in the RV-3029.
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
20.0
0.0
-20.0
-40.0
-60.0
-80.0
-100.0
-120.0
-140.0
-160.0
-180.0
-60
-40
-20
T₀ = 25°C (±5)
-0.035 ppm * (T-T0)² (±10%)
0
20
40
60
T [°C]
80
100
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
Β: 2^nd order temperature coefficient -0.035 ppm * (T-T₀)² ±10% (quadratic thermal coefficient)
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