SH7708 datasheet(355/633 Pages) RENESAS

355 / 633 page

337

12.3.5

Crystal Oscillator Circuit

Crystal oscillator circuit constants (recommended values) are shown in table 12.5, and the RTC

crystal oscillator circuit in figure 12.5.

Table 12.5

Recommended Oscillator Circuit Constants (Recommended Values)

osc

out

32.768 kHz

10 to 22 pF

SH7708R

EXTAL2

XTAL2

XTAL

Cin

Cout

Notes: 1. Select either the Cin or Cout side for frequency adjustment variable capacitor

according to requirements such as frequency range, degree of stability, etc.

2. Built-in resistance value Rf (Typ value) = 10 MΩ, RD (Typ value) = 400 kΩ

3. Cin and Cout 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 12.5 Example of Crystal Oscillator Circuit Connection

SH7708 数据表(PDF) 355 Page - Renesas Technology Corp