SH7706 Datasheet, PDF (408/749 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH™ RISC engine Family/SH7700 Series

Section 13 Realtime Clock (RTC)
13.4.5 Crystal Oscillator Circuit
Crystal oscillator circuit constants (recommended values) are shown in table 13.2, and the RTC
crystal oscillator circuit in figure 13.5.
Table 13.2 Recommended Oscillator Circuit Constants (Recommended Values)
f
osc
32.768 kHz
C
in
10 to 22 pF
C
out
10 to 22 pF
SH7706
Rf
EXTAL2
XTAL
Cin
RD
XTAL2
Cout
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 Cin and Cout 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 13.5 Example of Crystal Oscillator Circuit Connection
Rev. 5.00 May 29, 2006 page 360 of 698
REJ09B0146-0500