s-35190a Seiko Instruments Inc., s-35190a Datasheet - Page 38

• Manufacturer Part Number: s-35190a
• Description: 3-wire Real-time Clock
• Manufacturer: Seiko Instruments Inc.

38
3-WIRE REAL-TIME CLOCK
S-35190A
3. Adjustment of oscillation frequency
(1) Adjustment by setting C
Matching of the crystal oscillator with the nominal frequency must be performed with the stray capacitance on the
board included. Select a crystal oscillator and optimize the C
*1 . Request a crystal manufacturer for matching evaluation between the IC and a crystal. The recommended
*2 . The C
*3 . Adjust the rotation angle of the variable capacitance so that the capacitance value is slightly smaller than the
Caution
crystal characteristic values are, C
k Ω max.
value in a range of 0 pF to 9.1 pF.
center, and confirm the oscillation frequency and the center value of the variable capacitance. This is done in
order to make the capacitance of the center value smaller than one half of the actual capacitance value because a
smaller capacitance value increases the frequency variation.
g
1. The oscillation frequency varies depending on the ambient temperature and power supply
2. The 32.768 kHz crystal oscillator operates more slowly at an operating temperature than higher
value must be selected on the actual PCB since it is affected by stray capacitance. Select the external C
voltage. Refer to “ Characteristics (Typical Data)”.
or lower 20 to 25 ° C. Therefore, it is recommended to set the oscillator to operate slightly faster
at normal temperature.
Fixed capacitor
NO
g
Select a crystal
capacitance
specification
YES
Figure 47 Crystal Oscillator Setting Flow
oscillator
Variable
START
Optimal
Set C
value
C
END
g
in
NO
YES
g
*2
L
*1
value (load capacitance) = 6 pF, R
Seiko Instruments Inc.
NO
YES
Change C
Trimmer capacitor
g
g
value in accordance with the flowchart below.
Make fine adjustment
variable capacitance
of frequency using
Set to center
capacitance
Frequency
of variable
1
YES
value (equivalent serial resistance) = 50
*3
NO
Rev.2.4
_00
g