L138 DDR2 controller: DQGATE resistor resistance

Anonymous

Hi,

I would like to ask a question on the resistor for OMAP L138 DDR2 controller’s DQGATE net class:

On p.139 of L138 datasheet there is no specification on resistor value.
In EVMAM1808 the combined resistance of two resistors (R282 & R283) is (10=10+0)Ω.
In Hawkboard it is marked as 0E, which I suspect might be 0Ω.

Is there any requirement on this? Why EVMAM1808 and Hawkboard are different on this?

Zheng

over 13 years ago

0 jc-ti over 13 years ago

TI__Mastermind 27585 points

Terminators are not required on the DQGATE nets.

Jeff

0 Anonymous over 13 years ago in reply to jc-ti

Jeff,

But both EVMAM1808 and Hawkboard has them, and I have put the footrpints for two resistors on the PCB board which means I have to add two resistors there. In signal integrity if the signal sees different instantaneous impedance as it travels, there would be reflection. So I guess I need to put resistors whose resistance is the same as the impedance of the trace connecting with it?

The trace connecting with the resistor has impedance 50Ω, so should I make both resistors 50Ω or each 25Ω?

Zheng

0 jc-ti over 13 years ago in reply to Anonymous

TI__Mastermind 27585 points

You may use 0-ohm resistors, since the resistors are optional.

Jeff

0 Anonymous over 13 years ago in reply to jc-ti

Jeff,

Thanks, I will do this accordingly.

Zheng

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L138 DDR2 controller: DQGATE resistor resistance