• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 760 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

LM317M: Maximum Output Current

Ryan Waite
Prodigy 10 points
Part Number: LM317M


Hello everyone,

I am attempting to determine the maximum output current for the LM317M across a range of input and output voltages.

Section 6.5 Electrical Characteristics of the datasheet provides the following information:

However, this information potentially conflicts with Figure 6 of the datasheet, which shows significantly higher output currents:

Manually computing the maximum output current via RθJA and power dissipation leads to more confusion:

Using this equation for I results in the following data table:

In summary, the Electrical Specification, Figure 6, and manually calculating maximum output current are all giving differing results. Which should I trust? 

Thank you for your help!

Ryan

  • 0
    TI__Guru 50025 points

    Hi Ryan,

    The maximum current in the EC table is listed as typical, so I don't think there is a discrepancy there.

    There is one issue with using T_J to calculate the max current as you have done - the maximum junction temperature is not 125C; i.e. it is recommended to not exceed 125C, but there is not thermal shutdown circuitry that will shut the part off if it exceeds 125C. So, the maximum current for each of these data points would likely be higher. 

    Figure 6 is real data, so I think that is what you should use. Of course, for Tj's between 25C and 125C you can expect the curves to be between the 25C and 125C curves. 

    Best regards,

    Nick