RV5C339A Datasheet, PDF (32/51 Pages) RICOH electronics devices division – 3-WIRE SERIAL INTERFACE REAL-TIME CLOCK ICs WITH VOLTAGE MONITORING FUNCTION

RV5C339A
Course (A)
When the time count precision of each real-time clock is not to be adjusted, the crystal oscillator intended for use
with that real-time clock may have any CL value requiring no presetting. The crystal oscillator may be subject to
frequency variations which are selectable within the allowable range of time count precision. Several crystal
oscillators and real-time clocks should be used to find the center frequency of the crystal oscillators by the method
described in “2.2 Measurement of Oscillation Frequency” and then calculate an appropriate oscillation adjustment
value by the method described in “2.4 Oscillation Adjustment Circuit” for writing this value to the RV5C339A.
Course (B)
When the time count precision of each real-time clock is to be adjusted within the oscillation frequency variations of
the crystal oscillator plus the frequency variations of the real-time clock ICs, it becomes necessary to correct
deviations in the time count of each real-time clock by the method described in “2.4 Oscillation Adjustment Circuit”.
Such oscillation adjustment provides crystal oscillators with a wider range of allowable settings of their oscillation
frequency variations and their CL values. The real-time clock IC and the crystal oscillator intended for use with that
real-time clock IC should be used to find the center frequency of the crystal oscillator by the method described in
“2.2 Measurement of Oscillation Frequency” and then confirm the center frequency thus found to fall within the
range adjustable by the oscillation adjustment circuit before adjusting the oscillation frequency of the oscillation
circuit. At normal temperature, the oscillation frequency of the oscillator circuit can be adjusted by up to
approximately ±1.5ppm.
Course (C)
Course (C) together with Course (D) requires adjusting the time count precision of each real-time clock as well as
the frequency of 32.768-kHz clock pulses output from the 32KOUT pin. Normally, the oscillation frequency of the
crystal oscillator intended for use with the real-time clocks should be adjusted by adjusting the oscillation stabilizing
capacitors CG and CD connected to both ends of the crystal oscillator. The RV5C339A, which incorporate the CG
and the CD, require adjusting the oscillation frequency of the crystal oscillator through its CL value.
Generally, the relationship between the CL value and the CG and CD values can be represented by the following
equation:
CG × CD
CL =
+ CS
CG + CD
where “CS” represents the floating capacity of the printed circuit board
The crystal oscillator intended for use with the RV5C339A is recommended to have the CL value on the order of 6 to
8pF. Its oscillation frequency should be measured by the method described in “2.2 Measurement of Oscillation
Frequency”. Any crystal oscillator found to have an excessively high or low oscillation frequency (causing a time
count gain or loss, respectively) should be replaced with another one having a smaller and greater CL value,
respectively until another one having an optimum CL value is selected. In this case, the bit settings disabling the
oscillation adjustment circuit (see “2.4 Oscillation Adjustment Circuit”) should be written to the oscillation
adjustment register.
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