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4.17ExternalClockInputFromOscillatororCLKINPin
OSCV
DD
C
5
C
7
C
8
X
1
R
S
R
B
OSCIN
OSCOUT
C
6
OSCV
SS
CLKIN
Clock
Input
From
OSCIN
to
PLL
On-Chip 1.2-V Oscillator
(a)
External 3.3-V LVCMOS-Compatible Clock Source
(b)
OSCV
DD
OSCIN
OSCOUT
OSCV
SS
CLKIN
Clock
Input
From
CLKIN
to
PLL
CV
DD
(1.2 V)
NC
TMS320C6727,TMS320C6726,TMS320C6722
Floating-PointDigitalSignalProcessors
SPRS268E–MAY2005–REVISEDJANUARY2007
TheC672xdeviceincludestwochoicestoprovideanexternalclockinput,whichisfedtotheon-chipPLL
togeneratehigh-frequencysystemclocks.TheseoptionsareillustratedinFigure4-42.
•Figure4-42(a)illustratestheoptionthatusesanon-chip1.2-Voscillatorwithexternalcrystalcircuit.
•Figure4-42(b)illustratestheoptionthatusesanexternal3.3-VLVCMOS-compatibleclockinputwith
theCLKINpin.
NotethatthetwoclockinputsarelogicallycombinedinternallybeforethePLLsotheclockinputthatisnot
usedmustbetiedtoground.
Figure4-42.C672xClockInputOptions
Iftheon-chiposcillatorischosen,thentherecommendedcomponentvaluesforFigure4-42(a)arelisted
inTable4-38.
Table4-38.RecommendedOn-ChipOscillatorComponents
FREQUENCYXTALTYPEX
1
C
5
(1)
C
6
(1)
C
7
C
8
R
B
R
S
22.579AT-49KDS1AF225796A470pF470pF8pF8pF1MΩ0Ω
22.579SMD-49KDS1AS225796AG470pF470pF8pF8pF1MΩ0Ω
24.576AT-49KDS1AF245766AAA470pF470pF8pF8pF1MΩ0Ω
24.576SMD-49KDS1AS245766AHA470pF470pF8pF8pF1MΩ0Ω
(1)CapacitorsC
5
andC
6
areusedtoreduceoscillatorjitter,butareoptional.IfC
5
andC
6
arenotused,thenthenodeconnecting
capacitorsC
7
andC
8
shouldbetiedtoOSCV
SS
andOSCV
DD
shouldbetiedtoCV
DD
.
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