RV5C387A

PRELIMINARY

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14.2.

Configuration of Oscillation Circuit and Correction of Time Count Deviations

14.2.1.

Configuration of Oscillation Circuit

OSCIN

OSCOUT

VDD

VDD

32kHz

RD

RF

CG

CD

A

The oscillation circuit is driven at a constant voltage of approximately 1.2 volts relative to the level of the VSS

pin input.

As such, it is configured to generate an oscillating waveform with a peak-to-peak voltage on the

order of 1.2 volts on the positive side of the VSS pin input.

< Considerations in Handling Crystal Oscillators >

Generally, crystal oscillators have basic characteristics including an equivalent series resistance (R1)

indicating the ease of their oscillation and a load capacitance (CL) indicating the degree of their center

frequency.

Particularly, crystal oscillators intended for use in the RV5C387A are recommended to have a

typical R1 value of 30k

Ω and a typical CL value of 6 to 8pF. To confirm these recommended values,

contact the manufacturers of crystal oscillators intended for use in these particular models.

< Considerations in Installing Components around the Oscillation Circuit >

1) Install the crystal oscillator in the closest possible vicinity to the real-time clock ICs.

2) Avoid laying any signal lines or power lines in the vicinity of the oscillation circuit (particularly in the area

marked "A" in the above figure).

3) Apply the highest possible insulation resistance between the OSCIN and OSCOUT pins and the printed

circuit board.

4) Avoid using any long parallel lines to wire the OSCIN and OSCOUT pins.

5) Take extreme care not to cause condensation, which leads to various problems such as oscillation halt.

< Other Relevant Considerations >

1) For external input of 32.768-kHz clock pulses to the OSCIN pin:

DC coupling: Prohibited due to an input level mismatch.

AC coupling: Permissible except that the oscillation halt sensing circuit does not guarantee perfect

operation because it may cause sensing errors due to such factors as noise.

2) To maintain stable characteristics of the crystal oscillator, avoid driving any other IC through 32.768-kHz

clock pulses output from the OSCOUT pin.

Typical externally-equipped element

X’tal : 32.768kHz

(R1=30k

Ω typ)

(CL=6pF to 8pF)

Standard values of internal elements

RF

15M

Ω typ

RD

120k

Ω typ

CG,CD 12pF

typ