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SN74AHCT125-Q1: Slow Pin Behavior when xA tied to x/OE

Greg Amidon
Expert 5530 points
Part Number: SN74AHCT125-Q1
Other Parts Discussed in Thread: SN74LVC1G99-Q1, TXU0101-Q1

Tool/software:

Team,

My customer is using the AHCT125 and is concerned about slow inputs (slower than the datasheet max recommended 20ns/V.

Two questions:

1. Can a slow input cause damage to this device or just excessive power consumption?

2. Does the respective "x/OE" pin tied to the "xA" pin remediate this concern. I don't think so since the inputs will still be in the indeterminate state between 0.8 and 2V before /OE puts the output into Hi-Z, but please confirm.

Best regards,

Greg

  • 0
    Guru 316780 points

    1. There is no guarantee. When the input has slow edges, oscillations may occur, but they will eventually cease. Floating inputs would be worse.

    2. Correct; shoot-through currents happen at the input.

    There is no similar device with Schmitt-trigger inputs. The SN74LVC1G99-Q1 does not have TTL-compatible inputs. The TXU0101-Q1 has Schmitt-trigger inputs and can translate from a lower voltage, but requires two supplies and has an active-high enable input.