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LM2622 - DC/DC Converters at low/no load conditions and when Vout = Vin

dayberry
Prodigy 250 points
Other Parts Discussed in Thread: TPS61220, TPS61260, LM2622

So in my application I have a power source that is ideally at 3.6V but can drop as low as 2.6V while the circuity it powers needs a well regulated 3.6V. The load, however, is a pretty light typical amount of 5mA or so, though it can go up to 40mA. My question is what, in general, happens in a boost or buck-boost integrated circuit when the load current is considerably low like this? Also, what will happen in a boost converter IC in the case when the input voltage is already equal to the output voltage? For my application what would be a better topology to go with, the boost or the buck-boost?

  • 0
    TI__Guru**** 150610 points

    All of our converters operate well with little or no load, so that is not a question.  The bigger question is, what does a boost do when Vin > Vout.

    The answer is that it greatly depends on which specific device you are talking about.  Some have down regulation which keeps the output voltage regulated.  Others just pass Vin to Vout.

    In your case, with Vin = Vout with full batteries, you should be ok with just a boost as there will losses in the switching that will still keep it in boost mode.  I would recommend looking into the TPS61220 or TPS61260.  The TPS61260 offers down regulation while the TPS61220's performance with Vin > Vout is documented in a design note on this forum.

  • 0 in reply to Chris Glaser
    Prodigy 250 points

    Chris,

    Thanks for the incredibly fast response. Does that low/no load behavior also apply to the National line of converters, with LM prefixed part numbers? I am specifically looking at using the LM2622 boost converter IC.

    Would this boost IC also be OK when Vin = Vout or is slightly more than Vout?

  • 0 in reply to dayberry
    TI__Guru**** 150610 points

    If you're looking at a specific part, you need to put that part in the title of your post.  Please read the ground rules for this forum, located at the top of the forum.  Then, the appropriate apps engineer will respond.

  • 0 in reply to Chris Glaser
    Prodigy 250 points

    Well my original question was about converters IN GENERAL and not part specific, and after reading your initial response I THEN asked something about a specific part that I am looking at as AN OPTION. Considering my company uses hundreds of thousands of dollars worth of TI parts a year you'd think the employees would be a little more respectful and not so rude.

  • 0 in reply to dayberry
    TI__Guru**** 191445 points

    No intent to be rude.  We are just saying that if you have questions about specific parts. it is best to put them in the post title.  We have lots of engineers who specialize in specific product lines.  If you put the IC part number in the title, then the appropriate engineer may see it and respond.

    Thanks,

  • 0 in reply to JohnTucker
    Prodigy 250 points

    I have added the part number to the title.

    To reiterate my followup question to Chris, does the LM2622 behave well at low/no loads and would it be OK at conditions Vin = Vout or Vin = Vout + 50 mV?

  • 0 in reply to dayberry
    TI__Guru**** 150610 points

    Sorry, didn't mean to be rude.  Just letting you know the best way to get your question answered on the forums.  I also moved your part number to the front of your post title, since that is where is should go to be easily seen.

    I am not the engineer responsible for that IC.

    Your local FAE is the best first contact for these types of technical questions.  He can understand your entire system and make the best recommendations.