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Linux/TMDSEVM437X: DDR3 layout impedance Rtt

Part Number: TMDSEVM437X
Other Parts Discussed in Thread: AM4378

Tool/software: Linux

Hi,

       I will use four 8-Bit DDR3 Devices With VTT Termination.

       In the AM437X_GP_EVM_3K0006_PCB_REV1_4A.brd,in the Layout Cross Section window,if use 4mil width, the impedance is 58.148ohm on TOP layer and BOTTOM layer,54.671ohm on the L3_SIG1 and L4_SIG2.,and the Rtts are 47ohm. 

       For the DDR3 layout, in the Table 5-53 PCB Stackup Specifications in AM4378.pdf page 180 ,No.13,the signal-ended impedance,Zo,TYP50,MAX 75, Does it mean that I can use the signal-ened impedance Zo between 45 and 75,for example,60ohm,and the all the traces impedance between 55 and 65? and can I still use 47ohm for the Rtts? or which is the best?

     Best wishes,

Jianhua  Yuan