• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 2 answers
  • Subscribers 64 subscribers
  • Views 1307 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.

LM1117: Required Minimum Load Current For Regulation?

Gabriel Xu
Intellectual 2085 points
Part Number: LM1117

Hi LDO team

My customer is using LM1117-3.3 fixed output voltage version in their design.

I wondering to know are this device have requirement for minimum load current for output voltage regulation？

In datasheet I found such data for LM1117-ADJ (adjustable version) is 1.7mA under 25C. But fixed version spec didn't give out.

I also wondering to know why LM1117 or other legacy device need a minimum load current for regulation but our new generation products didn't have similar limitation?

  • 0
    TI__Mastermind 44790 points

    Hi Gabriel,

    The minimum load current for the ADJ is to make sure you size the R1/R2 resistors to maintain this minimum load requirement. FOr the fixed versions these resistors are internal and keep a minimum load. 

    To answer your question on why a minimum load current is required is because these older regulators are very simple designs and one of the risks is simply that leakage may cause VOUT to exceed the regulation voltage. Minimum load current can swamp out this effect. Modern regulators manage this more intelligently.

    The modern upgrade to any 1117 is the TLV767.

    Does this answer your question?

  • 0 in reply to JCHK
    TI__Intellectual 2085 points

    John

    I want to double confirm that the fixed version of LM1117 also has a minimum load current requirements. Is that right?

    And I still not clear the root cause of this phenomenon and where this "leakage current " flow through.

    Could you help me to figure it out through below internal circuit diagram? Thanks.

  • 0 in reply to Gabriel Xu
    TI__Mastermind 44790 points

    Hi Gabriel,

    Yes, the LM1117 also has a minimum load current.:

    For the fixed versions this is taken care of internally:

    You can think of this as the IQ for the device. Which is only 50uA in the TLV767.

    I hope this answers your question.

  • 0 in reply to JCHK
    TI__Intellectual 2085 points

    John

    I want to double confirm that the arrow direction is from the internal current source to Vout.

    Does it mean that this current will charge the output cap if load current is lower than this quiescent current and making the output voltage increase?

  • 0 in reply to Gabriel Xu
    TI__Mastermind 44790 points

    Hi Gabriel, 

    Yes, the arrow shows the internal low from VOUT to GND.

    I hope this clarifies your question.

  • 0 in reply to JCHK
    TI__Intellectual 2085 points

    Hi John

    Thanks for your help. No more questions from my side.