Texas Instruments TMS320DM355 warranty Oscillators and Clocks, 1 MXI1 24-MHz Oscillator

TMS320DM355

Digital Media System-on-Chip (DMSoC)

www.ti.com

SPRS463A –SEPTEMBER 2007 –REVISED SEPTEMBER 2007

5.5 Oscillators and Clocks

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].

5.5.1MXI1 (24-MHz) Oscillator

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.

MXI1/CLKIN		MXO1	VSS_MX1	VDDA_PLL1	VSSA_PLL1
				0.1	F
	Crystal
C1	24￿MHz￿or		C2	1	F
	36￿MHz
				L1

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.

CL	C1C2
	(C1	C2)

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