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SN74HC86A: A difference in the transition time between High and Low

Yuta Nishie
Genius 3625 points
Part Number: SN74HC86A
Other Parts Discussed in Thread: SN74HCS86, SN74HC86, TLV3202, TLV3502

Tool/software:

Hi,

I am using the SN74HC86APW in mass production, but after a certain Lot, there is a difference in the transition time between High and Low.

I would like you to confirm what is the cause of this and whether the difference is caused by the manufacturing Lot. I would like to send the circuit diagram and waveform, so could you handle it by private message?

Best Regards,

Nishie

  • 0
    Guru 279040 points

    PCN#20200629000.1 introduced an entirely new die. The guaranteed datasheet limits have not changed, but the new die has a smaller propagation delay and adds some hysteresis at the inputs.

    Are the input proper digital signals? I suspect that they do not go to VCC/GND, or that they violate the specified Δt/Δv limit. In the latter case, a device with Schmitt-trigger inputs (SN74HCS86) might help.

  • 0 in reply to Clemens Ladisch
    Genius 3625 points

    Hi Clemens-san,

    Thank you for your support.

    I understand that hysteresis has been added to the input, but could you tell me the value as a spec?

    Best Regards,

    Nishie

  • 0
    Genius 3625 points

    Hi,

    I would like to send the circuit diagram and input/output voltage waveform by private message. Is it possible for anyone to support me?

    Best Regards,

    Nishie

  • 0 in reply to Yuta Nishie
    Guru 279040 points

    For the SN74HC86(A), hysteresis is neither specified nor guaranteed. In theory, it could be as large as VIH − VIL, but in practice, it will be much smaller.

  • 0 in reply to Clemens Ladisch
    Genius 3625 points

    Hi Clemens-san,

    A simplified circuit diagram and each input/output waveform were measured to create a document for a symptom in which operation is different after a certain lot.
    Is this symptom related to PCN# 20200629000.1?

    SN74HC86APWR.pdf

    Best Regards,

    Nishie

  • 0 in reply to Yuta Nishie
    Genius 3625 points

    Hi TI team,

    If it is not related to PCN# 20200629000.1, please check the circuit diagram. Could someone please support me via private message?

    Best Regards,

    Nishie

  • 0 in reply to Yuta Nishie
    Guru 279040 points

    A plain logic device like the SN74HC86(A) is designed for logic signals, not for sine waves.

    • When the edges are slower than the specified Δt/Δv limit, then you must use a device with Schmitt-trigger inputs (e.g., SN74HCS86).
    • When the peaks of the sine wave do not reach the specified switching thresholds (VIL/VIH for plain inputs, or worst-case VT+/VT− for Schmitt-trigger inputs), then even a Schmitt-trigger device does not help, and you must use a comparator (e.g., TLV3202/TLV3502).

    But as far as I can see, your problem is also caused by the faster propagation delay of the newer die (the old die would not be capable of outputting such a short pulse). In any case, with a comparator, you have more control over the actual input switching threshold.