MSC8252 datasheet(56/68 Pages) FREESCALE

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MSC8252 Dual-Core Digital Signal Processor Data Sheet, Rev. 3

Hardware Design Considerations

Freescale Semiconductor

Each SerDes PLL power supply must be filtered using a circuit similar to the one shown in Figure 38, to ensure stability of the

internal clock. For maximum effectiveness, the filter circuit should be placed as closely as possible to the SRn_PLL_AVDD ball

to ensure it filters out as much noise as possible. The ground connection should be near the SRn_PLL_AVDD ball. The 0.003

μF

capacitor is closest to the ball, followed by the two 2.2

μF capacitors, and finally the 1 Ω resistor to the board supply plane. The

capacitors are connected from SRn_PLL_AVDD to the ground plane. Use ceramic chip capacitors with the highest possible

self-resonant frequency. All trances should be kept short, wide, and direct.

3.3

Clock and Timing Signal Board Layout Considerations

When laying out the system board, use the following guidelines:

•

Keep clock and timing signal paths as short as possible and route with 50

Ω impedance.

•

Use a serial termination resistor placed close to the clock buffer to minimize signal reflection. Use the following

equation to compute the resistor value:

Rterm = Rim – Rbuf

where Rim = trace characteristic impedance

Rbuf = clock buffer internal impedance.

Figure 37. PLL Supplies

Figure 38. SerDes PLL Supplies

MSC8156E

PLL0_AVDD

PLL1_AVDD

PLL2_AVDD

VDD Power Rail

(Voltage Regulator)

VSS

2.2

μF

2.2

μF

0.003

μF

SRn_PLL_AVDD

SRn_PLL_AGND

as short as possible

GNDSXC

VDDSXC

MSC8252 Datenblatt(PDF) 56 Page - Freescale Semiconductor, Inc

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