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lm2679 Vin min

leonardo belia
Prodigy 30 points
Other Parts Discussed in Thread: LM2679, LM5118

Hi all, i'm Leonardo from Italy

I'm new, and not so expert ^_^
I have 2 questions about ic lm2679

My english is not so good, so i haven't undestand from datasheet what happen if LOAD need more current than what i set with limit resistor. The devide turn off or just limit the output current up to the valor i set? 

The second question is about  minimun voltage input. My source are 2 lithium cell series configuration, for 7,4V (3,7+3,7). Datasheet says Vin range is 8-40V
Do u think is possible use lm2679 with only 7,4V ?

Are there others IC like this with lower Vin? 

Thank you so much for the help. Regards. 

  • 0
    TI__Genius 15810 points

    Hello Leonardo,

    If the load is increased beyond the set point, then the device starts to limit the current. This could also cause your output voltage to drop. Since the minimum input voltage on the LM2679 is 8V, it cannot function with voltages lesser than that. There are quite a few buck regulators that can operate down to 6V input and are newer than the LM2679. I would suggest you use Webench (http://webench.ti.com/webench5/power/webench5.cgi) for your purpose. You could enter your requirements and then the tool will suggest what regulators would be best suitable for your needs. I hope this information is helpful.

    Regards,
    Akshay 

  • 0 in reply to Akshay Mehta
    Prodigy 30 points

    Thank you so much for your help.

    I'm going crazy to find in TI database a IC with all requirements i need.
    I need adjustable UVLO, adj current and volt togheter.

    The most similar ic is LM22679-adj, but uvlo falling threshold is 3.9V, fixed and cant changed. ( i need about 5.5v )

    Someone know an ic like this but with adj uvlo? 

     

  • 0 in reply to leonardo belia
    TI__Genius 15810 points

    What are you exact input and output requirements? We could probably help in suggesting an IC to you.

    Regards,
    Akshay 

  • 0 in reply to Akshay Mehta
    Prodigy 30 points

    Hi, ty for so fast reply :D

    Ok, Vin are 2 cells lithium series, for 7.4V togheter
    I need an ic with Vin min lower of this value, so 1.25-5v should be good. Vin max higher that 2 cells series configuration, so >9V should be good.
    UVLO must be 5.5-6V, because these cells already have a pcm integrated protection, but under 3V performance become obsolete, so i want regulator stop to work under certain conditions.

    Vout min 1.25-2.5V, Vout max = Vin ( or at least >6.2V / >0.85*Vin )
    Iout >=3A
    Adj Current Limit, from 0 to Iout, <1.2A to Iout should be good too.

    I know are a lot of things for a single unit, by the way i hope TI have one :D 

  • 0 in reply to leonardo belia
    TI__Genius 15810 points

    I will look in to this and reply soon.

    Regards,
    Akshay 

  • 0 in reply to leonardo belia
    TI__Genius 15810 points

    Hello Leonardo,

    From what I understand, you need something that can handle input from 5V to >9V. Your load current is somewhere near 3A. Your output voltage seems to vary from 1.25 to >6.2V (or 85% of Vin). For these conditions, you will require a buckboost topology. I am not sure if you want a varying output voltage or not. But as such a voltage regulator cannot do that.

    You could use the LM5118 for your requirements because the LM5118 can operate in a buck and a buck-boost topology and has a UVLO option. You could use a resistor divider to set the UVLO threshold. I hope this information is helpful.

    Regards,
    Akshay