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SN74HC00: SN74HC00D, HC00

Obi Musturu
Prodigy 35 points
Part Number: SN74HC00
Other Parts Discussed in Thread: SN74HCS00

Tool/software:

Dear Texas Instruments Support Team,

We are experiencing inconsistencies in signal stretching behavior between different batches of the SN74HC00D NAND gate in our  product. Specifically, we observed that:

  • Older batches with line marking (e.g., TI 38CJJXK HC00, 18C49TK G4 HC00, 2BC8Z9K G4 HC00) exhibit proper stretching of around 4.9 to 5.3 ms.
  • Newer batches with dot marking (e.g., 32Z3VYJG3 HC00, TI 38CJJXK HC00) exhibit an increased stretching time of 6.2 to 6.5 ms , deviating from expected behavior.

Our setup involves [using SN74HC00D we make signal stretching of 5 ms when needed , e.g., RC delay circuit with (Capacitor, 100nF, X7R, 5% Tol, 0603, 25V, Resistor, 68k, 1% Tol, 0603, with supply voltage 4.92 V)]. Please check below schematic for reference. Also attached images of the Dot marked and Line marked SN74HC00D IC.

We would like to understand:

  1. Are there any functional differences or internal design changes between these batches?
  2. Could process variations or different internal die revisions affect propagation delay or threshold behaviour?
  3. Are there any recommended steps to mitigate these timing differences to ensure consistency?

We appreciate your insights into this matter, as it directly impacts our product performance. Please let us know if additional details or measurements are required.

Thanks in advance

  • 0
    Guru 318700 points

    The SN74HC00D was discontinued. But I'm assuming you're talking about the SN74HC00DR.

    The recommended operating conditions require an input rise/fall time of at most 500 ns. With 5 ms, correct operation is not guaranteed.

    1. Since PCN#20200629000.1, this device uses an entirely new die. The guaranteed datasheet limits have not changed, but typical characteristics have changed. In particular, the propagation delay is smaller, and the inputs have a small amount of hysteresis (changing the switching thresholds).
    2. Yes.
    3. Do not rely on characteristics that are not guaranteed by the datasheet. To be able to handle slow edges, use a device with Schmitt-trigger inputs (SN74HCS00) or a comparator. To get precise switching threshold, use a comparator.
      Alternatively, adjust the R/C values whenever there is a PCN.