Make 5vdc into 5.5vdc

Discussion in 'General Electronics Chat' started by Msahyouni, Feb 16, 2012.

  1. Msahyouni

    Thread Starter New Member

    Feb 16, 2012
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    im trying to use and LDO that gives out 3.6V, which i need for an LCD backlight and a dataflash. finding an LDO that outputs 3.6 is very hard and the only two available need 5.5V as input. all i have is 5V ?!!!
    how can i get that extra 0.5V without using an LDO or DC/DC converter.
    i need a solution that will not affect my current a lot too and that would give me a stable result.


    thanx in advance
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Here are are a number of LDOs that have less then 1V dropout so they can readily provide 3.6V from a 5V source.

    When you say the ones you found require 5.5V are your sure that isn't 5.5V maximum?
     
  3. Msahyouni

    Thread Starter New Member

    Feb 16, 2012
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    Thanks for the reply and the link, but in the link you sent me i cant see any ldo that takes in 5V and gives out 3.6V this is making me suspecious that i might be reading my datasheet wrong, although it says Vin = Vout+ 0.3 or 2v whichever is greater.

    So could you recommend on that gives the parameters im looking for ( preferrably fixed) so i could read its datasheet and figure out what i might be doing wrong!

    Thanx again
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    There are literally tons of LDO's that can run off 5V and put out 3.6V. You did not specify load current, you can't select one without knowing the load current.

    that's probably their maximum rating.
     
  5. Msahyouni

    Thread Starter New Member

    Feb 16, 2012
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    Well im sure there are tons, but i want to buy from farnell sweden, the current can be anywhere > 50mA
     
  6. t06afre

    AAC Fanatic!

    May 11, 2009
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    Farnell Sweeden have at least 10 regulators with output equal to 3.6 volt. The selection table is somewhat missleading "Primary Input Voltage" mean max inputvoltage. What is your max current need. And what do you prefer to work with SMD or DIL package?
     
  7. Msahyouni

    Thread Starter New Member

    Feb 16, 2012
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    You guys are making me feel as if i dont know how to read a datasheet. Well, maybe after 8-9 straight hrs of studying i really cant. Anyways, smd is fine, and it has to give out min 50-60 mA
    Thanx again
     
  8. t06afre

    AAC Fanatic!

    May 11, 2009
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    The LP2985AIM5-3.6 should do just fine then
     
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  9. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Msahyouni,
    You should really specify the MAX current not the min. >50mA means you could also need 1 or 10 or 50 or 100 Amps
     
  10. hspalm

    Active Member

    Feb 17, 2010
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    A low dropout regulator that drops 1.9v is not an LDO regulator. Try using digikeys search where you can narrow down parts on specifications. Most distributors have search features like that.
     
  11. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    You have to know the MAXIMUM load current to get an LDO.
     
  12. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Actually, it is. The "standard" regulators like 7805 or LM340 typically specify 2.5V (min) required to assure staying in regulation over full range of load and temp.

    The LT1085 type of design specs a dropout voltage of about 1.4V over full range, we called those "quasi LDO's". The true LDO's have dropout voltages of a volt or less.
     
  13. hspalm

    Active Member

    Feb 17, 2010
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    Must admit I didn't think much before answering. I'm currently implementing an LDO in my own project, need a 3.3v regulator at 150mA max and they have typical dropout voltages at 150mV!
     
  14. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    That's a pretty good LDO to get 150 mV @ 150 mA (one Ohm). Probably low voltage CMOS design with an internal charge pump?

    We had some cheap CMOS LDO's that could do dropouts under 1V with currents as high as 3A. It's not too hard to get the ON resistance of the FET down below 0.3 Ohms with the available MOS processes.
     
  15. Msahyouni

    Thread Starter New Member

    Feb 16, 2012
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    well after reading the datasheet that "t06afre" referred me to, it made me think that actually my LDO does work with the parameters i need (take in 5V and give out 3.6V), could anyone kindly confirm?!!! or did i read the datasheet right the first time and it does need 5.5V?!!

    the part is:TEXAS INSTRUMENTS - TLV70036DSET - LDO, 200MA, 6WSON
    you can just paste that in farnell and you'll see the part and datasheet

    thanx again guys
     
  16. t06afre

    AAC Fanatic!

    May 11, 2009
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    If you are 100% sure your current will always be below 150 mA. You can use this circuit it can handle input voltages up to 16 volt. Have you done some measurement to confirm this. If not just do it;) The maximum current is a parameter that is equally important to maximum input voltage. If your current is close to 150 mA select some other LDO. Remember to discuss the selection of the LDO in your report. Teachers love such details
     
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  17. crutschow

    Expert

    Mar 14, 2008
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    That device will work with an input voltage of up to a maximum of 6V. But the minimum voltage it needs is simply the maximum dropout voltage added to the output voltage. So at Io = 200mA the maximum dropout voltage is 250mV, thus the maximum input voltage you would need is 3.6V + .25V = 3.85V.
     
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