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LM317L: Thermal Parameters

Brian Wang0928
Genius 11970 points
Part Number: LM317L
Other Parts Discussed in Thread: LM317

The operation condition is 15Vin and 5Vout with 100mA in motor drive application.

We found there is a similar part from STM, LM317LD13TR. in which, the thermal resistance is much lower for SO8 package. Is it true? 

In the LM317L, the Theta_JA is about 97degree/W much higher than 55degree/W of the LM317LD13TR, correct?

Thermal is a critical parameter in this design. Is there any p2p compatible device with LM317LD13TR in this application? Thanks. 

Regards

Brian

  • 0
    TI__Mastermind 44070 points

    Hi Brian,

    The TJA numbers are not easy to compare as the above solution is not using a JEDEC standard High-K board (see footnote 1 in the above table). The JEDEC standard board is not optimized for thermal performance so it is relatively easy to improve on this metric with a decent layout. This application report shows how different layouts impact thermal performance.

    To answer your question if using a JEDEC Standard High-K board, I would think the TJA numbers would be a little closer. 

    I hope this answers your question.

  • 0 in reply to JCHK
    TI__Genius 11970 points

    In the ST's datasheet i attached, It said the SO-8 package used for voltage regulation is modified internally to have pins 2, 3, 6 and 7 electrically die attach flag. This particular frame decreases the total thermal resistance of the package and increase dissipate power when..... it looks this is a technique to improve the thermal resistance, correct? Does TI LM317 have the same technique to lower down the thermal resistance? Customer always choice a best device to use according to datasheet. If we can prove that our device has the same parameter of the thermal resistance. i think customer would have more confidence to use it. pls understanding. Very thanks. 

    Regards

    Brian

  • 0 in reply to Brian Wang0928
    TI__Mastermind 44070 points

    Hi Brian,

    I not sure about the internal construction of the ST part, but I can say that we too have an electrical connection to the die. It may be slightly better but the reason we use the JEDEC standard to show our TJA number is that it is an industry-standard. If we laid out a board with 6cm^2 copper pad and measured TJA our numbers would also improve. 

    Without having the ST part on hand we can only speculate on the actual difference between the two thermally. 

    Regards,

  • 0 in reply to JCHK
    TI__Genius 11970 points

    just double check with you. you mean that the die connections inside the device are the same between TI and ST (pins 2, 3, 6 and 7 electrically die attach flag), right?

    If so, the thermal performance should be exactly the same based on the same JEDEC standard, correct?

    Regards

    Brian

  • 0 in reply to Brian Wang0928
    TI__Mastermind 44070 points

    Hi Brian,

    We would have to perform a tear-down of the ST device to see whether or not there are actual differences. Normally it is the die size, and then the package that plays a primary role in thermal performance. 

    The key question I have is that if they have a real advantage, then why not report it using a standard JEDEC HIgh-K board like everyone else?

    Regards,