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TL751L: Enable disable pin

Neil Wilber
Prodigy 10 points
Part Number: TL751L
Other Parts Discussed in Thread: TL750L, LM2936, LM2931-N

This part is to be used in our design as an alternate part for the TL750.  Our design does not tie the enable disable pin to enable.  The datasheet does not say if the enable/disable pin has an internal pull down to keep the regulator enabled, if the pin is left floating.

Can you provide this detail?

  • 0
    TI__Guru 50025 points

    Hi Neil,

    It is probably a safe bet that this very old part does not have an internal pull up/down, but I will reach out to see if I can get you a more definitive answer. I suppose you are looking for a drop-in replacement for an already in-production board? 

    Regards,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 10 points

    Hi Nick,

    Yes this is an old design that's still in production.  Our manufacturer has asked if we can add the TL751 to our list of alternates.

    Regards,

    Neil

  • 0 in reply to Neil Wilber
    TI__Guru 50025 points

    Hi Neil,

    What package is the TL750 in? Also, just be clear you are referring to the "L" series for both TL750 and TL751, right? I.e. TL750L and TL751L. 

    Regards,

    Nick

  • 0 in reply to Neil Wilber
    TI__Guru 50025 points

    Hi Neil,

    Nevermind the first question. What are the operating requirements? The LM2936 and LM2931-N have P2P packages but whether they could work would depend on the required specs.

    Regards,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 10 points

    Hi Nick,

    I didn't tell you the whole story about the need to use the TL751L.  I'm not looking for other alternates, I just need to know if I can use the TL751L.  Because of an oversite, the buyer (overseas) has purchased a number of the TL751L.  So they have a large stock on hand they can use to continue production.  If the TL751L can used in a circuit that leaves the enable / disable pin floating.

  • 0 in reply to Neil Wilber
    TI__Guru 50025 points

    Hi Neil,

    I see. I had design look into this and the design files are not available. If they have a board they can populate with one of the TL751L's they can easily test whether the part has a pull up. Otherwise I am trying to locate some of them so I can try it myself. I am not sure that we have some of these lying around here but if we do I will get back to you by Tuesday next week. 

    Regards,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 10 points

    Hi Nick,

    Thanks for your help!  No need to test it, we have already tested it and it seems fine.  However I'm hesitant to make the call that it will be OK without a definitive answer on the default state of the enable pin. We'll come up with a solution such as rework or scrap the TL751L.  Once again appreciate your help.

  • 0 in reply to Neil Wilber
    TI__Guru 50025 points

    Hi Neil,

    Here is a test the designer suggested for confirmation of an internal pull up/down circuit:

    • If there is an internal pull-up, when EN=0V, there should be current out of the EN pin.
    • If there is an internal pull-down, when EN = 2V, there should be current into the EN pin.

    Hope this helps. 

    Regards,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 10 points

    Hi Nick,

    Makes sense, I did not think of that.  Thanks!