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LM317M: Maximum Allowable Losses

Ryu Yamashita
Genius 3685 points
Part Number: LM317M

Tool/software:

Hi team,

I cannot find a relationship between maximum allowable loss and temperature for this device.
Is there any information on these?

Regards,
Ryu.

  • 0
    TI__Guru 50025 points

    Hi Ryu,

    The maximum junction temperature is noted in section 6.3. The maximum internal power dissipation depends on the package used and the board layout, and you can typically find this information in the table in section 6.4 Thermal Information in our datasheets. Our thermal metrics are simulated using the JEDEC High-k board layout specified in JESD51-7; this board is not thermally optimized but serves as  standardized reference layout for easy comparisons of thermal performance. I'm not sure why there is only thermal data for the DCY (SOT-223) package; if you need the others I can submit a request to have them simulated. 

    Here are a couple app notes on this topic.

    An empirical analysis of the impact of board layout on LDO thermal performance: https://www.ti.com/lit/an/slvae85/slvae85.pdf

    Semiconductor and IC Package Thermal Metrics: https://www.ti.com/lit/an/spra953c/spra953c.pdf

    Regards,

    Nick

  • 0 in reply to Nick Butts
    Genius 3685 points

    Hi Nick,

    Thanks for the reply.
    Sorry what I want to know is the maximum PD.
    I would also like to know the relationship between PD and temperature.

    Regards,
    Ryu.

  • +1 in reply to Ryu Yamashita
    TI__Guru 50025 points

    Hi Ryu,

    Yes, my reply is referring to the more complicated issue of thermals, and I can't tell you the maximum power dissipation because there are many variables that affect how much power dissipation the device can handle (in particular, board layout, device package, and ambient temperature are the major influencers). In general it will look something like the diagram below for devices like the LM317M that have a high potential power dissipation (with VIN - VOUT max being 37V and 0.5A rated load current), but the slope is largely affected by the board layout and package thermal metrics. Do you know the max ambient temperature, max load current, and which package you are interested in for your application?

    Regards,

    Nick