
Category
Questions and Answers
Question 3:How many variation factors should be considered (Subject to use of fixed capacitors and
no adjustment of oscillation frequencies)
RP/RF/RS5C62
35
1. The possible factors behind oscillation frequency variations are :
1-1. Variations in frequencies of crystals,
1-2. Variations in oscillation characteristics of the ICs,
1-3. Variations in the external oscillatory capacitors C
G
and C
D
, and
1-4. Variations in floating capacitance present on the actual PCB.
2. On the other hand, the possible factors behind surrounding environment variations are :
2-1. Variations in ambient temperature, and
2-2. Variations in supply voltage.
Variations in 1 - 1 to 1 - 4 are listed in the order of decreasing degree. The individual variations
are described below :
1-1. Most crystals seem to have variations in their frequencies on the order of ±20ppm while
some crystals may have smaller variations. For variations in frequencies of individual crys-
tals, inquire of their suppliers.
1-2. Sample measurements of variations in oscillation characteristics of the ICs are shown
graphically on the next page. Note that these measurements are not guaranteed ones and
are therefore intended for reference use only.
1-3. Variations in oscillation frequencies differ slightly depending on the capacitance of external
oscillatory capacitors C
G
and C
D
. More specifically, the smaller the capacitance of C
G
and
C
D
, the greater the variations in oscillation frequencies. Subject to no adjustment of oscilla-
tion frequencies, they should have small variations relative to their capacitance (see the
graphs in 10.5 and 10.6 of “10. Typical Characteristics”).
1-4. Normally, variations in floating capacitance present on the actual PCB seem to be small
enough to be negligible.
2-1. Variations in ambient temperature are dominantly affected by the temperature characteris-
tics of fork-shaped crystal oscillators (forming an upward-facing quadratic curve) (see the
graph in 10.8 of “10. Typical Characteristics”).
2-2. Because the oscillatory circuit inside the ICs is driven by constant voltage, Variations in
oscillation frequencies due to variations in supply voltage measure±0.5ppm or less on real
terms at room temperature with the VDD pin input ranging from 2.5V to 5.5V (see the
graph in 10.7 of “10. Typical Characteristics”).