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54ACT logic device input latchup?

Has anyone seen a failure scenario where an input to a 54ACT device (54ACT244 pin 1A4, for example) is driven from logic '0' to logic '1', then stays at logic '1' after the source driver attempts to switch to logic '0'?

Thanks,

Jeff

  • Jeff,

    Can you clarify a little bit for me?

    Are you saying that the input pin is driven low and the output pin remains high?  Can you provide a schematic and scope shots of the issue?

  • We haven't made scope shots yet. The question is an attempt to explain what might be happening, based on evidence from reported failures, to help us make a test plan for the lab.

    Input pin 1A4 of the 54ACT244 is driven by pin Q5 of a SN74LVTH32373 part.

    The state of the 54ACT244 pin 1A4 is set to logic '1', then changed to logic '0'. At that point, one theory (or question) is that the 54ACT244 has a failure mode where pin 1A4 attempts to remain at logic '1' (a latchup inside the part?) and the SN74LVTH32373 part can't sink enough current from the 54ACT244 to reduce the line voltage below the logic '0' threshold.

    We'll go to the lab and try to get some more information.

    Thanks,

    Jeff

  • Jeff,

    The LVTH32373 has an internal bus hold circuit which allows the part to keep the most recent state on an input even if it is left floating, but the ACT244 does not.  The bus hold is like a weak pull-up (or pull-down) and should not cause issues if the input is being driven by another part.

    Without a schematic I'm not sure if I can be of much help.  Hopefully your lab tests will give us an answer.

  • After looking at some test data showing an address bit following another address bit some of the time, I inspected the board and found a solder bridge between two address lines. This was causing failures across the backplane.

    Due to a board-level test escape, the short circuit couldn't be detected.

    The failure had nothing to do with the 54ACT244 part.

    Thanks,

    Jeff