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6.5
Crystal Oscillator or External Clock Input
The C6745/6747 device includes two choices to provide an external clock input, which is fed to the on-
chip PLL to generate high-frequency system clocks. These options are illustrated in
Figure
6-7. For input clock frequencies between 12 and 20 MHz, a crystal with 80 ohm max ESR is
recommended. For input clock frequencies between 20 and 30 MHz, a crystal with 60 ohm max ESR is
recommended. Typical load capacitance values are 10-20 pF, where the load capacitance is the series
combination of C1 and C2.
The CLKMODE bit in the PLLCTL register must be 0 to use the on-chip oscillator. If CLKMODE is set to 1,
the internal oscillator is disabled.
•
Figure 6-6
illustrates the option that uses on-chip 1.2V oscillator with external crystal circuit.
•
Figure 6-7
illustrates the option that uses an external 1.2V clock input.
f
Oscillator frequency range (OSCIN/OSCOUT)
osc
Copyright © 2008–2014, Texas Instruments Incorporated
C
2
OSCIN
X
1
OSCOUT
C
1
OSCV
SS
Figure 6-6. On-Chip 1.2V Oscillator
Table 6-2. Oscillator Timing Requirements
PARAMETER
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Product Folder Links:
TMS320C6745 TMS320C6747
TMS320C6745, TMS320C6747
SPRS377F – SEPTEMBER 2008 – REVISED JUNE 2014
Clock Input
to PLL
MIN
12
Peripheral Information and Electrical Specifications
Figure 6-6
and
MAX
UNIT
30
MHz
69
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