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LM317M: PCB copper area Calculation For Power Dissipation

Aditya Yedur
Prodigy 140 points
Part Number: LM317M

Hello 

I need help 

I am using  part- LM317MDCYR to design power supply 

Input- 20V to 28V DC

Output -15V 100mA

Operating Ambient  temp - (-25 to 55 °C)

1) How should i calculate or consider the copper area Of LDO for Power Dissipation 

2) What should I consider  the Rθja for (1Layer ,2layer & 4Layer PCB)

Regards 

Aditya Yedur

  • 0
    TI__Genius 14245 points

    Hey Aditya, 

    1.3W of possible power dissipation is quite a bit from a thermal perspective. So your primary goal should be to maximize the amount of heat your PCB can dissipate (this would mean the lowest Rθja).

    Thermal dissipation can be complex, but the best thing you can do is add as much copper as possible around and connected to the LDO (this includes the other PCB layers). With a really optimized PCB layout you can improve thermal dissipation of an IC by 35%-50% compared the the JEDEC Standard which is reported in most data sheets (and all TI LDO datasheets). We have an app note which shows this with actual boards we built and tested, you can find that at this link. 

    https://www.ti.com/lit/an/slvae85/slvae85.pdf

    I'll also include a ppt I put together to help others which covers thermals, provides info on the JEDEC Standard, how design for good thermals and test then them on your PCB. It's not super long, but hopefully it helps. 

     LDO Thermal Performance.pdf