TMS320DM6435_16 Datasheet, PDF (158/252 Pages) Texas Instruments – Digital Media Processor

TMS320DM6435
Digital Media Processor
SPRS344C – NOVEMBER 2006 – REVISED JUNE 2008
6.6 External Clock Input From MXI/CLKIN Pin
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The DM6435 device includes two options to provide an external clock input:
• Use an on-chip oscillator with external crystal.
• Use an external 1.8-V LVCMOS-compatible clock input.
The optimal external clock input frequency is 27 MHz. Section 6.6.1 provides more details on Option 1,
using an on-chip oscillator with external crystal. Section 6.6.2 provides details on Option 2, using an
external 1.8-V LVCMOS-compatible clock input.
6.6.1 Clock Input Option 1—Crystal
In this option, a crystal is used as the external clock input to the DM6435.
The 27-MHz oscillator provides the reference clock for all DM6435 subsystems and peripherals. The
on-chip oscillator requires an external 27-MHz crystal connected across the MXI and MXO pins, along
with two load capacitors, as shown in Figure 6-9. The external crystal load capacitors must be connected
only to the 27-MHz oscillator ground pin (MXV_SS). Do not connect to board ground (V_SS). The MXV_DD pin
can be connected to the same 1.8 V power supply as DV_DDR2.
MXI/CLKIN
Crystal
27 MHz
MXO
MXV_SS
MXV_DD
C1
C2
1.8 V
Figure 6-9. 27-MHz System Oscillator
The load capacitors, C1 and C2, should be chosen such that the equation is satisfied (typical values are
C1 = C2 = 10 pF). C_L 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 (MXI and MXO) and to the MXV_SS pin.
C_L
+
C₁C₂
(C₁ ) C₂)
Table 6-13. Input Requirements for Crystal
PARAMETER
Start-up time (from power up until oscillating at stable frequency of 27
MHz)
Oscillaton frequency
ESR
Frequency Stability⁽¹⁾
MIN
TYP
27
MAX
4
60
±50
UNIT
ms
MHz
Ω
ppm
(1) For video and audio applications, stability of the input clock is very important. The user should select crystals with low enough ppm to
ensure good video and audio quality for the specific application.
158 Peripheral Information and Electrical Specifications
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