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TIDEP-01020: Maximum allowed stub length

Junpei Kishi
Intellectual 865 points
Part Number: TIDEP-01020

Hi team,

I would like to ask about maximum stub length in TIDEP-01020.

Following tidcfv7 gerber files, back drills have to cut Layer 5, but do not cut Layer 3.
Does it means that allowed stub length is 30.1 mil at maximum? (25.0mil of FR-4 between L4-5, 0.6mil of L4 copper, and 4.5mil of FR-4 between L3-4)

Best Regards,
Junpei Kishi

  • +1
    TI__Mastermind 39540 points

    I cannot confirm the maximum stub length, as each PCB design is different.  For this TI design, we minimized the stub by drilling to layer 5.  As discussed in the Jacinto7 LPDDR4 guidelines application note - it is recommended to control stub lengths for these high speed signals.  Our recommendation is for customers to perform simulations on their PCB to determine if via stub reductions (or other design trade-offs) are needed and to what extent.

  • 0 in reply to Robert Eschler
    TI__Intellectual 865 points

    Robert-san,

    Thanks for your replying.
    I understand the maximum stub length is changed in case by case, and TI suggests us following an app note and running a simulation.

    Best Regards,
    Junpei