• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 19 subscribers
  • Views 222 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

SN74LVC2GU04: Peak clamping current

SN74LVC2GU04: Output clamping specification

Alfred Fuchs1
Intellectual 320 points
Part Number: SN74LVC2GU04

In the Absolute maximum ratings the Output clamping current is given for the condition "Vo<0".(SCES197N )

This would indicate that there is no clamping diode to Vcc.

The same applies to 74LVC1G14 or 74LVC1G125 etc. 

In Nexperia's corresponding datasheet (Dual unbuffered inverter (nexperia.com)) the text is the same, but Fig. 3 shows a clamping diode to Vcc at the output.

But Nexperia's datasheet for the ..125 (Bus buffer/line driver; 3-state (nexperia.com)) specifies the Output clamping current for "VO > VCC or VO < 0 V" (without explaining picture), indicating a diode to Vcc.

This is the same what the TI datasheet says for 74LVC14, but not for the 74LVCU04, but Nexperia says it also for the 74LVCU04.

Actually I assume that LVC logic devices from these two manufacturers are created equal (essentially).

I do guess that there is a clamping diode at the output to Vcc and that the data sheet wording is unfortunate, but I am not sure any more.

Could it be that this is different for LVC and tiny LVC?

Could it be that this is different case by case?

Does the diode make sense for an output that is constantly on, to begin with? (IMHO it does in case of power-down.)

Properly speaking the capability of the output clamping to Vcc is unspecified.

What's the ground truth actually here? Who is going to clean up?

  • 0
    Guru 243910 points

    The output diode is not there for devices that have the partial power down (Ioff) feature.

    It is possible that this is a difference between TI and Nexperia. (It is also possible that at least one datasheet is wrong.)

  • 0 in reply to Clemens Ladisch
    Intellectual 320 points

    No Ioff anywhere in the datasheet.

  • 0 in reply to Alfred Fuchs1
    Guru 243910 points

    The SN74LVC2GU04 datasheet has it on page 1. (Only tiny LVC devices have it.)

  • 0 in reply to Clemens Ladisch
    Intellectual 320 points

    Right, it is mentioned there, but does not appear in the rest of the datasheet. Hm.

  • 0 in reply to Clemens Ladisch
    Intellectual 320 points

    Apparently many devices with 3-state outputs have it such as 74LVC244 etc. (according to https://www.ti.com/lit/ug/scbd152b/scbd152b.pdf)

    And the LV series has it.

    For the 74LVC2GU04 Nexperia does not mention it (though for 74LVC1G00 - standard logic - it is in the datasheet; and the diode is shown.).

    Does that really mean that TI and Nexperia devices are different in this respect?

    Or did someone forget to delete it on page 1 of the TI datasheet (where IMHO the specification is incomplete)?

    If there is such diversity then this is not nice (we pray five times daily for second sources ...).

  • +1 in reply to Alfred Fuchs1
    TI__Guru* 96591 points

    Hi Alfred,

    In this case, the error is that the SN74LVC2GU04 does not have the Ioff specification although it does say that on the front page. The datasheet has been marked to be updated, but it just hasn't been completed yet.

    I can't speak for Nexperia, but the TI device has an added negative clamp diode at the output, but no additional positive clamp diode.

    It is important to note, however, that the pFET does have a parasitic diode to the supply, so you will find that it can be back-powered from the output if the device is off. I would not recommend running any significant current through that diode.

    -

    If you're using these devices as regular logic inverters, I'd consider them direct replacements... but based on our previous conversation, I expect that you might be using this in a different manner -- and there's no telling how well matched the performance of the individual MOSFETs are from one manufacturer to another. I should also mention that, even if they are perfectly matched today, there's nothing stopping either company from releasing a new version that still meets the DS specs, but doesn't have exactly the same performance at some later date.