MPC8548E datasheet(67/143 Pages) FREESCALE

67 / 143 page

MPC8548E PowerQUICC III Integrated Processor Hardware Specifications, Rev. 8

Freescale Semiconductor

High-Speed Serial Interfaces (HSSI)

output driver features 50-

Ω termination resistor. It also assumes that the LVDS transmitter establishes its

own common mode level without relying on the receiver or other external component.

Figure 44. AC-Coupled Differential Connection with LVDS Clock Driver (Reference Only)

Figure 45 shows the SerDes reference clock connection reference circuits for LVPECL type clock driver.

Since LVPECL driver’s DC levels (both common mode voltages and output swing) are incompatible with

the MPC8548E SerDes reference clock input’s DC requirement, AC-coupling has to be used. Figure 45

assumes that the LVPECL clock driver’s output impedance is 50

Ω. R1 is used to DC-bias the LVPECL

outputs prior to AC-coupling. Its value could be ranged from 140 to 240

Ω depending on the clock driver

vendor’s requirement. R2 is used together with the SerDes reference clock receiver’s 50-

Ω termination

resistor to attenuate the LVPECL output’s differential peak level such that it meets the MPC8548E SerDes

reference clock’s differential input amplitude requirement (between 200 and 800 mV differential peak).

For example, if the LVPECL output’s differential peak is 900 mV and the desired SerDes reference clock

input amplitude is selected as 600 mV, the attenuation factor is 0.67, which requires R2 = 25

Ω. Consult a

clock driver chip manufacturer to verify whether this connection scheme is compatible with a particular

clock driver chip.

Figure 45. AC-Coupled Differential Connection with LVPECL Clock Driver (Reference Only)

SD_REF_CLK

Clock Driver

100

Ω Differential PWB Trace

CLK_Out

LVDS CLK Driver Chip

10 nF

MPC8548E

SerDes Refer.

CLK Receiver

Clock Driver

SD_REF_CLK

Clock Driver

100

Ω Differential PWB Trace

SerDes Refer.

CLK Receiver

Clock Driver

CLK_Out

LVPECL CLK Driver Chip

MPC8548E

10 nF

CLK_Out

Clock Driver

MPC8548E Datasheet(PDF) 67 Page - Freescale Semiconductor, Inc

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