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5.5 Oscillators and Clocks

5.5.1

MXI1 (24-MHz) Oscillator

Crystal

24MHzor

36MHz

MXI1/CLKIN

MXO1

VSS_MX1

0.1 F

1 F

VDDA_PLL1

VSSA_PLL1

1C2

TMS320DM355

Digital Media System-on-Chip (DMSoC)

SPRS463 – SEPTEMBER 2007

has two oscillator input/output pairs (MXI1/MXO1 and MXI2/MXO2) usable with external crystals or

ceramic resonators to provide clock inputs. The optimal frequencies for the crystals are 24 MHz

(MXI1/MXO1) and 27 MHz (MXI2/MXO2). Optionally, the oscillator inputs are configurable for use with

external clock oscillators. If external clock oscillators are used, to minimize the clock jitter, a single clean

power supply should power both the and the external oscillator circuit and the minimum CLKIN rise and

fall times must be observed. The electrical requirements and characteristics are described in this section.

The timing parameters for CLKOUT[3:1] are also described in this section. The has three output clock pins

(CLKOUT[3:1]). See Section 3.5 and Section 3.6 for more information on CLKOUT[3:1].

The MXI1 (typically 24 MHz, can also be 36 MHz) oscillator provides the primary reference clock for the

device. The on-chip oscillator requires an external crystal connected across the MXI1 and MXO1 pins,

along with two load capacitors, as shown in Figure 5-5. The external crystal load capacitors must be

connected only to the oscillator ground pin (VSS_MX1). Do not connect to board ground (VSS). Also, the PLL

power pin (VDDA_PLL1) should be connected to the power supply through a ferrite bead, L1 in the example

circuit shown in Figure 5-5.

Figure 5-5. MXI1 (24-MHz) Oscillator

The load capacitors, C1 and C2, should be chosen such that the equation is satisfied (typical values are

C1 = C2 = 10 pF). CL in the equation is the load specified by the crystal manufacturer. All discrete

components used to implement the oscillator circuit should be placed as close as possible to the

associated oscillator pins (MXI1 and MXO1) and to the VSS_MX1 pin.

Peripheral Information and Electrical Specifications

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