Basic Clock Module Operation
4-8
Basic Clock Module
Using an External Resistor (R
OSC
) for the DCO
The DCO temperature coefficient can be reduced by using an external resistor
R
OSC
tied to DV
CC
to source the current for the DC generator. Figure 4−6
shows the typical relationship of f
DCO
vs. temperature for both the internal and
external resistor options. Using an external R
OSC
reduces the DCO
temperature coefficient to approximately 0.1%/C. See the device-specific data
sheet for parameters.
R
OSC
also allows the DCO to operate at higher frequencies. For example, the
internal resistor nominal value is approximately 300 kΩ, allowing the DCO to
operate up to approximately 5 MHz. When using an external R
OSC
of
approximately 100 kΩ the DCO can operate up to approximately 10 MHz. The
user should take care to not exceed the maximum MCLK frequency specified
in the datasheet, even though the DCO is capable of exceeding it.
Figure 4−6. DCO Frequency vs. Temperature
Celsius
0 50 100
−25%
0
25%
−50
Internal
External
f
DCO