em3027 EM Microelectronic, em3027 Datasheet - Page 7

• Manufacturer Part Number: em3027
• Description: Real-time Clock With I2c Or Spi Interface, Crystal Temperature Compensation, Battery Switchover And Trickle Charger
• Manufacturer: EM Microelectronic

4.3
A frequency of the real crystal is dependent on the
temperature concurring with the following diagram:
T
F
Example 1: Qcoef=0.035; T
Copyright © 2008, EM Microelectronic-Marin SA
07/08 – rev B
O
O
-50
Δ F
F
– Turnover temperature in [°C]
– Crystal frequency when T
O
[ppm]
Crystal Thermal Behaviour
-200
-300
-400
-100
Figure 1 – Crystal thermal behaviour
0
-200
-400
-600
600
400
200
T
O
0
-100
R
0
[ppm]
T
O
-50
Temperature [°C]
O
50
O
Compensation Value
Crystal Error
=25; XtalOffset=–100
T
O
T
O
100
+50
Temperature
T
T [°C]
O
+100
150
The following formula expresses a compensation value
to be used during frequency correction.
Qcoef
T
T
XtalOffset
COMP_val
The Oscillator Frequency is adjusted, according to the
equation above by using coefficients located in the
EEPROM control page and a temperature.
The actual temperature can be obtained from the internal
thermometer or from Temp register updated externally by
an application.
A principle of the frequency compensation is based on
the adding/removing of pulses.
Example 2: Qcoef=0.035; T
7
-50
O
COMP_val
-100
-200
-300
-400
400
300
200
100
0
0
=
– Thermal quadratic coefficient [ppm/°C
– Actual temperature in [°C]
– Turnover temperature in [°C]
– Crystal offset at T
– Compensation value result in [ppm]
[ppm]
Qcoef
×
(T
50
O
Compensation Value
Crystal Error
=25; XtalOffset=+100
−
To)
www.emmicroelectronic.com
O
EM3027
2
[ppm]
−
XtalOffset
100
Temperature
2
]
150