Texas Instruments TMS320C6722, TMS320C6727 External Clock Input From Oscillator or Clkin Pin

TMS320C6727, TMS320C6726, TMS320C6722

Floating-Point Digital Signal Processors

www.ti.com

SPRS268E –MAY 2005 –REVISED JANUARY 2007

4.17 External Clock Input From Oscillator or CLKIN Pin

The C672x 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 4-42.

∙Figure 4-42(a) illustrates the option that uses an on-chip 1.2-V oscillator with external crystal circuit.

∙Figure 4-42(b) illustrates the option that uses an external 3.3-V LVCMOS-compatible clock input with the CLKIN pin.

Note that the two clock inputs are logically combined internally before the PLL so the clock input that is not used must be tied to ground.

C5

OSCVDD

C7

OSCIN

X1

RB

C8RS

OSCOUT

C6

OSCVSS

CLKIN

On-Chip 1.2-V Oscillator

	CVDD (1.2 V)
	OSCVDD
	OSCIN
Clock		Clock
		Input
Input
	NC	From
From
		CLKIN
OSCIN	OSCOUT
		to
to
		PLL
PLL
	OSCVSS
	CLKIN

External 3.3-V LVCMOS-Compatible Clock Source

(a) (b)

Figure 4-42. C672x Clock Input Options

If the on-chip oscillator is chosen, then the recommended component values for Figure 4-42(a) are listed in Table 4-38.

Table 4-38. Recommended On-Chip Oscillator Components

FREQUENCY	XTAL TYPE	X	C (1)	C (1)	C	C	R	R
		1	5	6	7	8	B	S
22.579	AT-49	KDS 1AF225796A	470 pF	470 pF	8 pF	8 pF	1 MΩ	0 Ω
22.579	SMD-49	KDS 1AS225796AG	470 pF	470 pF	8 pF	8 pF	1 MΩ	0 Ω
24.576	AT-49	KDS 1AF245766AAA	470 pF	470 pF	8 pF	8 pF	1 MΩ	0 Ω
24.576	SMD-49	KDS 1AS245766AHA	470 pF	470 pF	8 pF	8 pF	1 MΩ	0 Ω

(1)Capacitors C5 and C6 are used to reduce oscillator jitter, but are optional. If C5 and C6 are not used, then the node connecting capacitors C7 and C8 should be tied to OSCVSS and OSCVDD should be tied to CVDD.

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