EM3027SDSTP14B datasheet(8/28 Pages) EMMICRO

Part #	EM3027SDSTP14B

Description	Real Time Clock with I2C or SPI, Crystal Temperature Compensation, Battery Switchover and Trickle Charger

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Manufacturer	EMMICRO [EM Microelectronic - MARIN SA]

Direct Link	http://www.emmicroelectronic.com

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R

EM3027

12/09 – rev D

8

www.emmicroelectronic.com

4.4

Crystal Calibration

In order to compensate temperature dependency of the

used crystal, correct values of XtalOffset, Qcoef and TO

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:

1) Supply the chip from VCC pin.

2) Set FD0 = FD1 = ‘0’. Set CLKOE pin to ’1’.

This provides the uncompensated

frequency signal from the crystal oscillator

directly on pin CLKOUT.

3) Measure output frequency fO at different

temperatures (at least five measurements

in equidistant points in the whole desired

temperature range are recommended).

Please note that quartz crystal needs few

minutes to stabilise its frequency at a given

temperature.

4) Compute frequency deviation ferr of output

frequency fo from the ideal (target)

frequency fL = 32.768Hz in all measured

points as follows:

ferr = (fo-fL)/fo .

5) Find a quadratic regression of the

measured dependency in form:

ferr = -c1(T – c2)

2 + c3 or fO = aT2 + bT + c.

6) Then real values of the searched

parameters can be obtained from the

following relations:

Qcoefreal = c1 = -a,

T0_real = c2 = -b/(2a),

XtalOffsetreal = c3 = c – b

2/(4a).

7) The values to be stored in EEPROM

Control Page have to be corrected in the

following way:

Qcoef = 4096*(1.05*Qcoefreal),

T0 = T0_real - 4,

XtalOffset = 1.05*XtalOffsetreal.

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