TMS320DM355_07 Datasheet, PDF (99/158 Pages) Texas Instruments – Digital Media System-on-Chip (DMSoC)

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TMS320DM355
Digital Media System-on-Chip (DMSoC)
SPRS463B – SEPTEMBER 2007 – REVISED OCTOBER 2007
5.5 Oscillators and Clocks
DM355 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 DM355 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 DM355 has three output
clock pins (CLKOUT[3:1]). See Section 3.5 and Section 3.6 for more information on CLKOUT[3:1].
5.5.1 MXI1 (24-MHz) Oscillator
The MXI1 (typically 24 MHz, can also be 36 MHz) oscillator provides the primary reference clock for the
DM355 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 (V_{SS_MX1}). Do not connect to board ground (V_SS). Also, the PLL
power pin (V_{DDA_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
V_{SS_MX1}
Crystal
C1
24 MHz or C2
36 MHz
V_{DDA_PLL1}
V_{SSA_PLL1}
0.1 F
1F
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 V_{SS_MX1} pin.
C_L
C₁C₂
(C₁ C₂)
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DM355 Peripheral Information and Electrical Specifications
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