RS5C372A Datasheet, PDF (39/59 Pages) RICOH electronics devices division – I2C bus SERIAL INTERFACE REAL-TIME CLOCK ICs

RS5C372A/B
2. Configuration of Oscillating Circuit and Time Trimming
2.1 Configuration of Oscillating Circuit
RS5C372A/B
VDD
VDD
8
RF
CG
RD _CD
OSCIN
7
32kHz
6
OSCOUT
A
Typical external device:
X'tal: 32.768kHz or 32.000kHz
(R1=30kΩ TYP.)
(CL=6pF to 8pF)
Typical values of internal devices:
RF 15MΩ (TYP.)
RD 60kΩ (TYP.)
CG, CD 10pF (TYP.)
The oscillation circuit is driven at a constant voltage of about 1.2V relative to the Vss level.
Consequently, it generates a wave form having a peak-to-peak amplitude of about 1.2V on the positive side of the Vss
level.
Considerations on Crystal Oscillator
Basic characteristics of a crystal oscillator includes R1 (equivalent series resistance: ease of oscillation) and
CL (load capacitance: rank of center frequency). R1=TYP. of 30kΩ, CL=6 to 8pF is recommended for the
RS5C372A/B. Confirm recommended values to the manufacturer of the crystal oscillator used.
Considerations in Mounting Components Surrounding Oscillating Circuit
1) Mount the crystal oscillators in the closest possible position to the IC.
2) Avoid laying any signal or power line close to the oscillation circuit (particularly in the area marked with
“← A →” in the above figure).
3) Apply the highest possible insulation resistance between the OSCIN or OSCOUT pin and the PCB.
4) Avoid using any long parallel line to wire the OSCIN and OSCOUT pin.
5) Take extreme care not to cause condensation, which leads to various problems such as oscillation halt.
Other Relevant Considerations
1) When applying an external input of clock pulses (32.768kHz or 32.000kHz) to the OSCIN pin:
DC coupling : Prohibited due to mismatching of input levels.
AC coupling : Permissible except that unpredictable results may occur in oscillator halt sensing due to
possible sensing errors caused by noises, etc.
2) Avoid using the oscillator output of the RS5C372A/B (from the OSCOUT pin) to drive any other IC for the
purpose of ensuring stable oscillation.
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