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

Yuta Nishie

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

3 months ago

0 Clemens Ladisch 3 months ago

Guru 294210 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 Yuta Nishie 3 months ago in reply to Clemens Ladisch

Genius 4020 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 Yuta Nishie 3 months ago

Genius 4020 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 Clemens Ladisch 3 months ago in reply to Yuta Nishie

Guru 294210 points

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

0 Yuta Nishie 3 months ago in reply to Clemens Ladisch

Genius 4020 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 Yuta Nishie 3 months ago in reply to Yuta Nishie

Genius 4020 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

+1 Clemens Ladisch 3 months ago in reply to Yuta Nishie

Guru 294210 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 (V_IL/V_IH for plain inputs, or worst-case V_T+/V_T− 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.

0 Yuta Nishie 3 months ago in reply to Clemens Ladisch

Genius 4020 points

Hi Clemens-san,

Thank you for your support.

First, I understand that this logic IC does not support sinusoidal waves. I would like to consider the IC with the parts number you suggested.

Also, regarding the change of propagation delay due to the change of die, I checked PCN#20200629000.1, but SN74HC86APWR was not mentioned. Can I assume that this PCN supports SN74HC86APWR?

20200629000.1.pdf

20200629_NonA.pdf

Best Regards,

Nishie

0 Clemens Ladisch 3 months ago in reply to Yuta Nishie

Guru 294210 points

I looked up the PCN on Mouser; that one lists the SN74HC86PWR: mouser.com/PCN/Texas_Instruments_PCN20200629000_20200630155743328.pdf

0 Yuta Nishie 3 months ago in reply to Clemens Ladisch

Genius 4020 points

Hi Clemens-san,

I would like to check if the SN74HC86APWR with "A" is listed in the PCN. Can I assume that the SN74HC86PWR and the SN74HC86 "A" PWR are the same?

Best Regards,

Nishie

+1 Clemens Ladisch 3 months ago in reply to Yuta Nishie

Guru 294210 points

The -A datasheet does not get updates; see [FAQ] What is the difference between the SN74HCxx and the SN74HCxxA? You should always look at the non-A datasheet/product page instead.

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