TMS320F28055 Datasheet, PDF (35/143 Pages) Texas Instruments – Piccolo Microcontrollers

TMS320F28055, TMS320F28054, TMS320F28053
TMS320F28052, TMS320F28051, TMS320F28050
www.ti.com
SPRS797 – NOVEMBER 2012
2.7.1 Internal Zero-Pin Oscillators
The F2805x 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 5.2.1 for more information on these oscillators.
2.7.2 Crystal Oscillator Option
The typical specifications for the external quartz crystal (fundamental mode, parallel resonant) are listed in
Table 2-19. Furthermore, ESR range = 30 to 150 Ω.
Table 2-19. Typical Specifications for External Quartz Crystal⁽¹⁾
FREQUENCY (MHz)
5
R_d (Ω)
2200
10
470
15
0
20
0
(1) C_shunt should be less than or equal to 5 pF.
C_L1 (pF)
18
15
15
12
C_L2 (pF)
18
15
15
12
XCLKIN/GPIO19/38 X1
Turn off
XCLKIN path
in CLKCTL
register
C_L1
Crystal
X2
R_d
C_L2
Figure 2-8. 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.
XCLKIN/GPIO19/38
X1 X2
External Clock Signal
NC
(Toggling 0−V_DDIO)
Figure 2-9. Using a 3.3-V External Oscillator
Copyright © 2012, Texas Instruments Incorporated
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