RV5C339A Datasheet, PDF (30/51 Pages) RICOH electronics devices division – 3-WIRE SERIAL INTERFACE REAL-TIME CLOCK ICs WITH VOLTAGE MONITORING FUNCTION

RV5C339A
2. Configuration of Oscillation Circuit and Correction of Time Count Deviations
2.1 Configuration of Oscillating Circuit
RV5C339A
VDD
VDD
10
RF
CG
RD _CD
OSCIN
9
32kHz
8
OSCOUT
A
Typical externally-equipped element
X'tal: 32.768kHz
(R1=30kΩ TYP.)
(CL=6pF to 8pF)
Standard values of internal elements
RF=15MΩ TYP.
RD=120kΩ TYP.
CG, CD=12pF TYP.
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 with the RV5C339A is recommended to have a
typical R1 value of 30kΩ and a typical CL value of 6 to 8pF. To confirm these recommended values, contact
the manufacturers of crystal oscillators intended for use with 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.
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