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13.3.5
Crystal Oscillator Circuit
Crystal oscillator circuit constants (recommended values) are shown in table 13.5, and the RTC
crystal oscillator circuit in figure 13.5.
Table 13.5 Recommended Oscillator Circuit Constants (Recommended Values)
fosc
32.768 kHz
SH7709S
Notes: 1. Select either the C
according to requirements such as frequency range, degree of stability, etc.
2. Built-in resistance value R
3. C
and C
in
when using a ground plane.
4. The crystal oscillation settling time depends on the mounted circuit constants,
floating capacitance, etc., and should be decided after consultation with the
crystal resonator manufacturer.
5. Place the crystal resonator and load capacitors C
to the chip.
(Correct oscillation may not be possible if there is externally induced noise in the
EXTAL2 and XTAL2 pins.)
6. Ensure that the crystal resonator connection pin (EXTAL2, XTAL2) wiring is
routed as far away as possible from other power lines (except GND) and signal
lines.
Figure 13.5 Example of Crystal Oscillator Circuit Connection
Cin
10 to 22 pF
R
f
EXTAL2
XTAL
C
in
or C
side for the frequency adjustment variable capacitor
in
out
(Typ value) = 10 MΩ, R
f
values include floating capacitance due to the wiring. Take care
out
Cout
10 to 22 pF
R
D
XTAL2
C
out
(Typ value) = 400 kΩ
D
and C
as close as possible
in
out
429
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