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Testing the SN74LVT244DBW

Brian Fowler
Prodigy 10 points

I am testing an SN74LVT244DBW using a Hutron Model 32, which is a the military version of the 3200S.  When probing any input pin (in relation to ground) I get what appears to be distortion starting at about 12V.  That is, the signature produces random, unstable current levels where the base signature is 0V and no current.  I liken it to the crackling distortion you might hear when you overdrive your speakers.  I know the answer is to not test these above 12 volts, but I was hoping some engineer could comment on this.  The test signals are 15V, 10K ohms and 200 Hz and 20V, 50K ohms and 200Hz.

Thanks!

Brian Fowler

NUWC DET FEO NORFOLK

  • +1
    Guru 316700 points

    If I'd have to guess, I'd suspect that the gate isolation breaks down in some place, but that the resulting current burns out the defect.

    Anyway, at any voltage above the absolute maximum rating (7 V), electromigration will degrade the device.

  • +1
    TI__Guru* 97046 points

    Hey Brian,

    I agree with Clemens's educated guess.  We have tried running voltages up to 20V on the inputs of different devices to see what happens, and generally speaking they will survive a bit above the absolute maximum rating, but beyond 12V I saw many of them fail in a short through the input gates. As long as the current is limited, they don't fail completely and often recover and function normally after returning to reduced voltages.

    I certainly wouldn't recommend connecting any voltage above 7V to the input of SN74LVT244 though -- that's likely to degrade the device and reduce reliability.

  • 0 in reply to Emrys Maier
    Prodigy 10 points

    Thanks for the reply.  The signal we use to test these are current limited, but I have always been concerned about testing devices well above their design range, these more so than others.

    Thanks again!

    Brian