• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 62 subscribers
  • Views 317 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.

LM5118: internal current limit threshold

Che yi Su
Expert 1695 points
Part Number: LM5118

Hi,

A described for "internal current limit threshold" in datasheet, but  I can't find the value. Could you help me to check value and how to transfer to Vcs(th) and Vcs(thx)? I need formula to calculate peak current when I use different  value of current sense resistor. THX! 

  • 0
    TI__Mastermind 21720 points
    Hi Che,

    Please refer to figure 2 of the datasheet. Please note that the current limit will change base on the input to output ratio. To size the inductor properly it is best to base it on boost mode operation as this is when the inductor current will be the largest. To do the simple calculation please use the LM5118 quick start calculator

    Thanks,

    Garrett
  • 0 in reply to Garrett Roecker
    Expert 1695 points

    Hi Garrett,

    Thanks for reply. Figure 2 is mean current limit by buck or boost mode. Please refer to yellow line, it's looks LM5118 has two level protection for different current rate. 

  • 0 in reply to Che yi Su
    TI__Mastermind 21720 points
    Hi Che,

    The two levels are the same. Note that the graph is referencing the voltage across the current sense pins while the text you have highlighted is referencing the internal signal. The two values differ by a factor of ~10. This is due to the current sense amplifier which has a gain of 10.

    The current limit changes based on the mode of operation. In boost mode it is 2.5V (internal) and in buck mode the limit is 1.25V (internal). During buck-boost mode the current limit transitions between the buck and boost limits accordingly. This is the intended operation because the current limit is keep close to the actual peak current during the transition region.

    Thanks,

    Garrett