Question about PCB impedance of OMAP-L138

Masato Miyashiro

Hi,

My customer is suffering, so I want to your help.

Table 6-29(P139) of the datasheet shows the DDR2 memory pattern constraint Single-ended impedance Zo is described as 50 to 75 Ω, but there is no description about differential impedance.

I think that the DDR_CLKP and DDR_CLKN lines are differential signals, are there restrictions on the differential impedance to be adjusted with the pattern?
(For example, if Zo = 60 Ω, can it be 2 x Zo = 120 Ω ?)

Also, is it OK to recognize that the terminating resistance is unnecessary?

Please give me if you have any information.

Best Regards,
Miyashiro

over 8 years ago

0 Senthilkumar Srinivasan over 8 years ago

TI__Mastermind 43660 points

Miyashiro,

You can consider 100 ohms for differential routing.

Yes, as mentioned in the datasheet, No terminations of any kind are required in order to meet signal integrity and overshoot requirements. However, please ensure that all the guidelines given in the datasheet are implemented in the layout.

Regards,
Senthil

0 Masato Miyashiro over 8 years ago in reply to Senthilkumar Srinivasan

Expert 1500 points

Hi Senthil,

Thank you for quick reply.
I will answer this information to my customer.

Best Regards,
Miyashiro

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Question about PCB impedance of OMAP-L138