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SN74HC132: Output Failing and Shorting VCC supply to ground

Ed Wilinski
Prodigy 30 points
Part Number: SN74HC132

We have the 74HC132 configured as two S-R Flip-Flop circuits on Board A. The outputs are connected through a pluggable ribbon cable to a M74HC4051TTR Mux Inputs with a 100K pull-up resistor to 3.3V on Board B. Board B generates its own 3.3V supply but shares a common ground with board A.

The failure that we are seeing is the 74HC132 output fails and shorts the VCC pin to ground. The failure occurs when we do 40 hour burn-in of multiple Board B boards but Board A w/132 is the same. We hot-plug Board B via the ribbon cable into Board A.

We have been using the HC132 in Board A for 14 years and been performing hot-plugging of Board B into A all that time. But we have been getting failures of the HC132 in the past two years. We can't understand why in the past two years the HC132 is failing like this and would like insight into the cause of failure.

Thanks,

Ed

  • 0
    TI__Mastermind 22285 points

    Hi Ed, 

    Do you have any schematics of your design and scope shots you can share of the failure?

  • 0
    Guru 257000 points

    Since about two years, TI is using new dies with smaller structures. It is plausible that the new devices are more sensitive to overvoltage.

    (Please note that the ESD and arcing caused by hotplugging were always exceeding the absolute maximum ratings, and that the old devices also got degraded. You were just lucky that the damage was not yet noticeable.)

    You need to add protection components like clamping diodes, TVS diodes, and/or current-limiting resistors. Their design depends on how much overvoltage actually happens and on the required drive strength and signals frequencies.