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SN74HC541: Multiple failure occurs due to short

saravana kumar
Prodigy 10 points
Part Number: SN74HC541
Other Parts Discussed in Thread: SN74HCS541

Tool/software:

Multiple failure is occurs due to short in this Buffer

Duration: Past 2years in different board with same application

failure rate: Multiple times

Note: power supply has been isolated by optocoupler

so kindly give the solution for the same.

  • 0
    Guru 316860 points

    These R-C filters have a time constant of 4.7 ms. This makes the edges much too slow; they violate the specified Δt/Δv limit. To fix this, use a device with Schmitt-trigger inputs like the SN74HCS541.

    Another possible reason is the output load, which is not shown in this schematic.

    Another possible reason is ESD. Can any of the input or output lines be touched, or are they connected to a board that is hot-(un)plugged?

  • 0 in reply to Clemens Ladisch
    Prodigy 10 points

    These R-C filters have a time constant of 4.7 ms. This makes the edges much too slow; they violate the specified Δt/Δv limit. To fix this, use a device with Schmitt-trigger inputs like the SN74HCS541.

    --> we have fixed digital input of 5V via RC filters, this input not occur frequently, so time delay is more and frequency not fixed. Based on this time-constant not important for us

    Another possible reason is the output load, which is not shown in this schematic.

    --> Input of the buffer comes from Optocoupler with isolated GND(5V) and output of the buffer goes to Flash Memory and MCU.

    Another possible reason is ESD. Can any of the input or output lines be touched, or are they connected to a board that is hot-(un)plugged?

    -->We does not perform any Hot-plugging

  • 0 in reply to saravana kumar
    Guru 316860 points

    What matters is not the time between edges, but the time needed for one edge. It violates the Δt/Δv limit. This can damage the chip; see [FAQ] How does a slow or floating input affect a CMOS device?

    Are there any other components (resistors, capacitors etc.) connected to the outputs?