S-35390A Seiko Instruments, S-35390A Datasheet - Page 35

• Manufacturer Part Number: S-35390A
• Description: 2-Wire Real Time Clock
• Manufacturer: Seiko Instruments

Rev.1.2
3. Adjustment of oscillation frequency
(1) Adjustment by setting C
Caution 1. The oscillation frequency varies depending on the ambient temperature and power
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
with the flowchart below.
_00
*1. For the matching adjustment of the IC with a crystal, contact the crystal manufacturer to
*2. The C
*3. Adjust the rotation angle of the variable capacitance so that the capacitance value is slightly
<Fixed capacitor>
determine the C
pF and R
Select the external C
smaller than the 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.
2. The 32 kHz crystal oscillator operates more slowly at an operating temperature than
higher or lower 20 to 25 ° C. Therefore, it is recommended to adjust or set the
oscillator to operate slightly faster at normal temperature.
supply voltage. Refer to the characteristics examples.
g
value must be selected on the actual PCB since it is affected by stray capacitance.
1
= 30 k Ω typ. are recommended values.
NO
L
Select a crystal oscillator
Figure 39 Crystal Oscillator Setting Flow
value (load capacitance) and R
g
YES
YES
g
specification?
value in a range of 0 pF to 9.1 pF.
capacitance
Is it optimal
START
Set C
Variable
value?
Is C
END
g
Seiko Instruments Inc.
in
NO
g
*2
NO
YES
Change C
*1
<Trimmer capacitor>
1
g
value (equivalent series resistance). C
2-WIRE REAL-TIME CLOCK
Make fine adjustment
variable capacitance
variable capacitance
of frequency using
Does frequency
Set to center of
match?
g
YES
value in accordance
S-35390A
NO
*3
L
= 6
35