Rev. 2.00, 09/03, page 372 of 690
15.4.5
Crystal Oscillator Circuit
Crystal oscillator circuit constants (recommended values) are shown in table 15.2, and the RTC
crystal oscillator circuit in figure 15.5.
Table 15.2
Recommended Oscillator Circuit Constants (Recommended Values)
f
osc
C
in
C
out
32.768 kHz
10 to 22 pF
10 to 22 pF
This LSI
EXTAL2
XTAL2
XTAL
C
in
C
out
R
f
R
D
Notes: 1. Select either the C
in
or C
out
side for frequency adjustment variable capacitor
according to requirements such as frequency range, stability, etc.
2. Built-in resistance value R
f
(Typ value) = 10 M
Ω
, R
D
(Typ value) = 400 k
Ω
3. C
in
and C
out
values include stray capacitance due to the wiring. Take care when
using a ground plane.
4. The crystal oscillation settling time depends on the mounted circuit constants,
stray capacitance, etc., and should be decided after consultation with the crystal
resonator manufacturer.
5. Place the crystal resonator and load capacitors C
in
and C
out
as close as possible
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 15.5 Example of Crystal Oscillator Circuit Connection
Содержание SH7705
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