em3027 EM Microelectronic, em3027 Datasheet - Page 8

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

4.4
In order to compensate temperature dependency of the used crystal properly, correct values of XtalOffset, Qcoef and T
parameters shall be stored in EEPROM Control Page. User is advised to follow these steps in order to compute the
parameters in a correct way:
Copyright © 2008, EM Microelectronic-Marin SA
07/08 – rev B
Crystal Calibration
1)
2)
3)
4)
5)
6)
Supply the chip from V
Set FD0 = FD1 = ‘0’. Force CLKOE pin to ’1’. This provides the uncompensated frequency directly from the
crystal oscillator on pin CLKOUT.
Measure output frequency f
whole considered temperature range are recommended).
Find a quadratic regression of the measured dependency in form: f
Then real values of the searched parameters can by obtained from the following relations:
Qcoef
T
XtalOffset
Values to be stored in EEPROM Control Page have to be corrected in the following way:
Qcoef = 4096*(1.05*Qcoef
T
XtalOffset = 1.05*XtalOffset
R
0_real
0
= T
real
= c
0_real
= c
2
real
= -b/(2a),
- 4,
1
= c
= -a,
3
= c – b
CC
2
/(4a).
pin.
real
O
real
),
at different temperatures (at least five measurements in equidistant points in the
.
8
O
= -c
1
(T – c
2
)
2
+ c
3
www.emmicroelectronic.com
or f
EM3027
O
= aT
2
+ bT + c.
O