Datasheet
ExternalClockSignal
(Toggling0−V
DDIO
)
XCLKIN/GPIO19/38
X2
NC
X1
X2X1
Crystal
XCLKIN/GPIO19/38
Turn off
XCLKIN path
in CLKCTL
register
R
d
C
L1
C
L2
TMS320F28027, TMS320F28026, TMS320F28023, TMS320F28022
TMS320F28021, TMS320F28020, TMS320F280200
SPRS523J –NOVEMBER 2008–REVISED OCTOBER 2013
www.ti.com
3.7.1 Internal Zero Pin Oscillators
The F2802x devices contain two independent internal zero pin oscillators. By default both oscillators are
turned on at power up, and internal oscillator 1 is the default clock source at this time. For power savings,
unused oscillators may be powered down by the user. The center frequency of these oscillators is
determined by their respective oscillator trim registers, written to in the calibration routine as part of the
boot ROM execution. See Section 6, Electrical Specifications, for more information on these oscillators.
3.7.2 Crystal Oscillator Option
The typical specifications for the external quartz crystal (fundamental mode, parallel resonant) are listed in
Table 3-16. Furthermore, ESR range = 30 to 150 Ω.
Table 3-16. Typical Specifications for External Quartz Crystal
(1)
FREQUENCY (MHz) R
d
(Ω) C
L1
(pF) C
L2
(pF)
5 2200 18 18
10 470 15 15
15 0 15 15
20 0 12 12
(1) C
shunt
should be less than or equal to 5 pF.
A. X1/X2 pins are available in 48-pin package only.
Figure 3-11. Using the On-chip Crystal Oscillator
NOTE
1. C
L1
and C
L2
are the total capacitance of the circuit board and components excluding the
IC and crystal. The value is usually approximately twice the value of the crystal's load
capacitance.
2. The load capacitance of the crystal is described in the crystal specifications of the
manufacturers.
3. TI recommends that customers have the resonator/crystal vendor characterize the
operation of their device with the MCU chip. The resonator/crystal vendor has the
equipment and expertise to tune the tank circuit. The vendor can also advise the
customer regarding the proper tank component values that will produce proper start up
and stability over the entire operating range.
Figure 3-12. Using a 3.3-V External Oscillator
42 Functional Overview Copyright © 2008–2013, Texas Instruments Incorporated
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