SH7727 Datasheet, PDF (549/1109 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7700 Series

Section 16 Realtime Clock (RTC)
16.3.5 Crystal Oscillator Circuit
Crystal oscillator circuit constants (recommended values) are shown in table 16.5, and the RTC
crystal oscillator circuit in figure 16.5.
Table 16.5 Recommended Oscillator Circuit Constants (Recommended Values)
fosc
32.768 kHz
Cin
10 to 22 pF
Cout
10 to 22 pF
SH7727
R_f
EXTAL2
XTAL
C_in
R_D
XTAL2
C_out
Notes: 1. Select either the C_in or C_out side for frequency adjustment variable capacitor
according to requirements such as frequency range, degree of stability, etc.
2. Built-in resistance value R_f (Typ value) = 10 MΩ, R_D (Typ value) = 400 kΩ
3. C_in and C_out values include floating capacitance due to the wiring. Take care
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_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 16.5 Example of Crystal Oscillator Circuit Connection
Rev. 5.00 Dec 12, 2005 page 477 of 1034
REJ09B0254-0500