TMX320C6720RFP300 datasheet(102/118 Pages) TI

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4.17 External Clock Input From Oscillator or CLKIN Pin

OSCVDD

OSCIN

OSCOUT

OSCVSS

CLKIN

Clock

Input

From

OSCIN

PLL

On-Chip Oscillator

(a)

External 3.3-V LVCMOS-Compatible Clock Source

(b)

OSCVDD

OSCIN

OSCOUT

OSCVSS

CLKIN

Clock

Input

From

CLKIN

PLL

CVDD

TMS320C6727B, TMS320C6726B, TMS320C6722B, TMS320C6720

Floating-Point Digital Signal Processors

SPRS370E – SEPTEMBER 2006 – REVISED JULY 2008

www.ti.com

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 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.

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 4-40.

Table 4-40. Recommended On-Chip Oscillator Components

FREQUENCY

XTAL TYPE

(1)

22.579

AT-49

KDS 1AF225796A

470 pF

8 pF

1 M

Ω

22.579

SMD-49

KDS 1AS225796AG

470 pF

8 pF

1 M

Ω

24.576

AT-49

KDS 1AF245766AAA

470 pF

8 pF

1 M

Ω

24.576

SMD-49

KDS 1AS245766AHA

470 pF

8 pF

1 M

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.

Peripheral and Electrical Specifications

102

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