RS5C313 Datasheet, PDF (22/32 Pages) RICOH electronics devices division – ULTRA-COMPACT REAL-TIME CLOCK IC

RS5C313
7. Oscillation Frequency Adjustment
7.1 Oscillation Frequency Measurement
VDD
OSCIN
OSCOUT
INTR
CE
VSS
32kHz
CG
+5V or +3V
Frequency
counter
1) When switch the CE pin to the high level after low level or
open state, a 1-Hz interrupt pulse is output from the INTR
pin about 2.5 seconds later. Measure this interrupt pulse by
using a frequency counter
2) Ensure that the frequency counter has more than six digits
(on the order of 1 ppm).
3) Place the CG between the OSCIN pin and the VSS level and
pull up the INTR pin output to the VDD .
7.2 Oscillation Frequency Adjustment
Select crystal oscillator *¹
(For fixed capacitance)
(For variable capacitance)
Change CL
value of crystal.
NG
Fix CG.
*²
Optimize CG.
OK
End
*³
Fix the capacitance of CG.
Optimize central variable
capacitance value
Change the CL
*^{3 value of crystal.}
NG
OK
Make fine frequency adjustment
with variable capacitance.
End
*1) To ensure that the crystal is matched to the IC, inquire its crystal supplier about its CL (load capacitance) and R1 (equivalent series resistance) val-
ues. It is recommended that the crystal should have the CL value range of 6 to 8pF and the typical R1 value of 30k ohms.
*2) To allow for the possible effects of floating capacitance, select the optimum capacitance of the CG on the mounted PCB. The standard and recom-
mendable capacitance values of the CG range from 5 to 24pF and 8 to 20pF, respectively. When you need to change the frequency to get higher
accuracy, change the CL value of the crystal.
*3) Collate the central variable capacitance value of the CG with its oscillation frequency by adjusting the angle of rotation of the variable capacitance of
the CG in such a manner that the actual variable capacitance value is slightly smaller than the central variable capacitance value. (It is recommended
that the central variable capacitance value should be slightly less than one half of the actual variable capacitance value because the smaller is vari-
able capacitance, the greater are fluctuations in oscillation frequency.) In the case of an excessive deviation of the oscillation frequency from its
required value, change the CL value of the crystal.
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